I doubt Vicente Guerrero ever visited the United States, but I will let someone who is more knowledgeable about that specific detail to address it.
What I would like to address, though, is a related topic which is the racism that Vicente Guerrero likely experienced in Mexico. Spanish colonial racial hierarchy and classification was very different than the racial black-white binary we know from US history. For example, a black man at the end of the colonial period in Mexico could be a slave or free, but regardless he belonged to the "Kingdom of the Spanish", and did not belong to the subordinate "Kingdom of the Indians." Also a black man, up until the 19th century could enroll in the Royal and Pontifical University of Mexico, and join the army (contrast this with the situation in the US). The effect of all of this is that there was perhaps a surprising social mobility in Mexico for black men, as compared to the US.
Add to this general context the fact that Vicente Guerrero was president of Mexico before the age of photography and would not have been seen in person by the majority of the population. Notice also that in paintings made of him, stereotypical black features were either downplayed (I suspect this is true) or that he was also of European and Indigenous descent (also highly probable). Now, finally, add to that that he distinguished himself in the military and came to the presidency for the first time less than 2 years after Mexican Independence, but already after over 10 people had preceded him in power. Important to note here is that he was not voted into office. To say the least, it was an extremely volatile political moment in which many people were parading through the highest office.
What I am saying is that Vicente Guerrero almost certainly suffered what we would today identify as racism for being black. But what complicates that statement is that anti-black racism in Mexico has historically functioned differently than elsewhere, because of the legacy of Spanish racial categories, because of a notion of racial mixing (mestizaje), because of the history of colonizing an area with a very large indigenous population, because of the history of forcibly immigrating fewer African slaves than in United States and the Carribean, and because black Mexicans were for the most part not formally barred from institutions such as the University and the army.
Edit: Thank you so very much kind stranger!
It seems almost certain that Guerrero didn't leave Mexico for at least two reasons: he was president only about 8 months between 1829-30, and was hanged the year after. And he spent most of that time trying to govern and... well not get overthrown. Oh and he fought back a Spanish reconquest attempt too.
The Mexican War of Independence was a long drawn out and very bloody affair, starting in the early 19th century, and was only slowly winding down. After the emperor Iturbibe was deposed there was long line of presidents which wasn't over even with the war hero Guerrero, as has been mentioned. So we can see how going the US would have been the first thing on the president's mind, also since there was not exactly any special friendly relations with the northern neighbour even then. Ie I couldn't find anything on Guerrero traveling at that time, would be interested of anyone did find something.
I would add that in colonial Mexico there was comparatively major participation of indigenous and African people during the independence wars, partly because of the regions long history of intermixing since the Spanish first landed. An earlier major leader, Morelos, was of mixed indigenous descent.
And so it's no accident that he (drawing on Hidalgo) made one of most advanced declarations in the western atmosphere then, that included abolishment of all slavery. And it's no accident that Guerrero - probably of mixed African descent, with debates on it ongoing - could hold a leading military position as general, and finally made true part of Morelos declaration by ending slavery.
This seems a bit anti climactic so I'm adding an earlier answer of mine on a related topic: the abolishment of Mexican slavery and US slaves who fled to Mexico.
In colonial Mexico aka New Spain slavery was an important institution from the beginning, as overall in the Americas. The demographic crisis of the native population meant an increase of African slaves brought to New Spain, with Cortés initating the first transport in the early 1520s. Slaves formed a crucial part of the colonial economy, although many managed to escape and formed settlements throughout central America, often living together with native groups, sometimes throughout colonial times (their descendants form an important part of today's Afro-Mexicans).
African slavery also worked differently in Spanish America than in the US, with overall many slaves working in households, though slaves did also had to do harsher work for example in gold mining. So that manumission was much more common in Spanish America than in the US or Brazil - with about 50% freed black population and 50% slaves by the 17th century.
Africans continued to stay on the lowest rung of colonial society and were heavily discriminated against, as are their descendants today. But the colonial casta system did allow for more social advances than say , the One Drop rule. In contrast with official views, many avenues were open to reach higher positions to black people. Current research highlights that ones position in society often depended on cultural factors - including habits, ones clothes and food, or even the practice of magic - that could be influenced, within the system's limits.
By the 18th century population growth among indigenous people together with an increasing mixed population made slavery less important, so that by some estimates at the time of independence in 1821 only about 3.000 were left in New Spain, with a very small number of them in Coahuila-Texas.
The Mexican War of Independence meant a re-settling of the northern border, with a new border set up by Spain in the US already in 1819. It also impacted on the issue of slavery there. The early main leaders of independence, Hidalgo and Morelos had both in different ways called for slavery's abolishment. During the short presidency Vicente Guerrero slavery was abolished in 1829. Guerrero himself was the first North American president of mixed descent, including African heritage.
While the Hidalgo movement had lost momentum early on, antislavery rhetoric continued throughout the 1820s, with no Mexican slaveholders to object. However, treaties passed during the late 1820s were quite ambiguous, e.g. with Texas being exempt from the abolishment of slavery.
The abolishment in Mexico led to different reactions among northern slaves, with Coahuila-Texas now a slaveholding society: some went looking for freedom further South in Coahuila or Tamaulipas. Others looked to the burgeoning slaveholding regions for escape, which were still more sparsely settled at that time. But a few years later the only choice left was to cross the Río Grande. Mexican equivocal attituted towards slavery led to Mexico taking a special place in slave's imaginations. Slaves would routinely reinterpret pronouncements made by the Mexican government, forming Mexico into a symbol of non-slavery. In addition the Mexican pronouncements further led to Texan slaveowners viewing Mexico as a poteintial threat.
With tensions between Texas and Mexico boiling over in the 1830s, increasing numbers of slaves fled south. While some of them were sent further south, others had less luck and were sent back to the north - always depending on the Mexican general in charge. Nonetheless, "as with the issue of legality, what mattered was not the actual policy, but the significance slaves attached to Mexican equivocation. To them, the Mexican Army was an army of liberation." (Kelley, Mexico In His Head": Slavery and the Texas-Mexico Border 1810-1860*)
With the anexation of Texas, slaves continued to escape south, probably numbering in the thousands. While both state and private individuals undertook expeditions to bring fugitives back, Mexican opposition tended to squash such attempts.
But there was also resistance by the slaves themselves, taking different forms: a slave revolt took place in 1835 at the Brazos river, brokend down by the militia. And a supposed plot by 200 local slaves to kill their masters was discovered in 1856 in central Texas, leading to the hanging of three "leaders". Since this fits well with fears of supposed slave rebellions in the Americas it's hard to say how much of this plot was real, but it again shows the linking of Mexico with antislavery discourses.
Even after 1845 then, Mexico continued to be viewed by slaves as a republic built on a more inclusive model of citizenship - a view that can cetrainly be debated, but certainly speaks to better perspectives at least for people of African descent there compared to the Jim Crow South.
Regarding the continuing Río Grande crossings, Roseann Bacha-Garza observes that often families and towns would help escaped slaves, providing them with resources, money and food. Due to the region's complex history there seems to have been more empathy for escaped slaves than in other southern regions. However military forts were also present along the river, remnants of the Mexican-American War. Officials at these forts were instructed to capture and return any slaves to their owners, but the structures were far from each other, making a clear border patrol difficult to maintain.
Sean Kelley notes that even into the late 18th and early 19th centuries, communities of slaves continued to appropriate the language of freedom across the Americas, drawing on a variety of subversive texts:
Among these texts were political boundaries, not only the Mexican border, but the Haitian coast, the Mason-Dixon Line, the Ohio River, and eventually the picket lines of the Union army. Slaves were among the world's most persistent border crossers. [Kelley, 719]
Still it's important to not see this as too rosy. In colonial times the Spanish were at the topic of the social hierarchy, indigenous people had certain protections and Africans were either slaves or as freedman had some rights. Racism against black and indigenous people has very deep roots in Mexico too.
The marginalisation of Afro Mexicans in Mexico continues until today. Black history is not well known compared to the "official" versions of events like the wars of independence. And, in brief, Afro Mexicans were only added to the official census a few years ago, including voting rights, evidence of a continuing and willful blind spot in the society.
For more on Africans in colonial Latin America and especially Mexico see also this (longish) answer of mine.
edit: added two paragraphs
There's a great answer by /u/The_Alaskan about the more general issue of black diplomats visiting the United States, but he focused on the 20th century and did not address Vicente Guerrero in particular.