In short, yes the Visigoths and Ostrogoths were most certainly different peoples. The Visigoths are most likely the Thervingi Goths who crossed the Danube in 376, while the Ostrogoths are likely the Greuthungi who crossed after the Thervingi Though it should be said that there is not enough evidence to definitively prove this, and there was probably some mixing of peoples between the two tribes after 376 (Especially before Alaric's, who was Thervingi, first invasion of Italy). But that being said there were most certainly two separate tribes of Goths inside the Roman Empire after 378.

The Thervingi Goths arrived on the shores of the Danube in the summer of 376 after their king, Athanaric, had been defeated by the Huns. A large number of Thervingi led by Frittergern then rebelled and migrated to the Danube:

So led by Alavivus (Alavivus led alongside Fritigern but was later killed) the Thervingi spread themselves over the banks of the Danube, and sent agents to Valens, humbly begging to be admitted to his dominions (Ammianus Marcellinus, The Later Roman Empire 31.3)

Valens, who was in Persia fighting the Sassanids at this time, eventually gave the Thervingi permission to cross into the Empire at least partially because his advisers convinced him it was a good idea:

The affair seemed mater for rejoicing...and the practiced flatters in the emperor's entourage extolled in exaggerated terms the good fortune which unexpectedly presented him with a large body of recruits (Ammianus Marcellinus, The Later Roman Empire 31.4)

As such the Thervingi were ferried across the Danube by the Roman forces stationed there. Valens had given the Thervingi land in Thrace to live on, but for the time being they had to remain near the Danube until they could be moved. The Thervingi quickly grew restless, however, and the commander of Thrace, Lupicinus, decided to move them closer to the city of Marcianople. But in order to do this he needed the entirety of the Danube Garrison which very quickly led to serious issues. Shortly after this the Greuthungi Goths (this is not Ammianus' first mention of the Greuthungi, I'm just not using him in chronological order) arrived on the shores of the Danube and asked for permission to cross the River. Their request was rejected however, but because the garrison was busy moving the Thervingi the Greuthungi crossed the river anyway. They would eventually join Frittigern and the Thervingi after the Thervingi rebellion at Marcianople (which of course led to the Battle of Adrianople).

​

Now as for the Greuthungi gefore 376, they were second group to be attacked by the Huns (after the Alans). After the Huns conquered the Alans, who bordered the Greuthungi, they made a pact of "friendship" with the survivors (most likely they became subjects of the Huns), and set their eyes on the territory of the Greuthungi. According to Ammianus the Greuthungi were very wealthy and King Ermenrich was a highly feared warrior. It is more likely that the Greuthungi were simply the next people to encounter the Huns because they lived immediately next to the Alans. Ermenrich killed himself after hearing rumors of the Huns and was succeeded by Vithimir, who was eventually killed in battle. This led to the Alatheus and Saphrax, who may actually have been an Alan, to move the Greuthungi to the Dneister (from where they would eventually migrate to the Danube). The defeat of the Greuthungi is what led to Athanaric to make camp near the Dneister to meet the Huns in battle. But as previously mentioned he was defeated and many of his people rebelled.

So even before the Vesi and Ostrogoths existed there were already different tribes of Goths, who were probably just confederations of related Gothic tribes, that lived beyond the Danube. Sometime after the Battle of Adrianople (378) the Goths began to identify themselves as Visigoths and Ostrogoths.

The Visigoths were the Goths led by Alaric (who was almost certainly never "King of the Goths") that were living in Illyricum in the early 400s. As i stated earlier many historians, believe that the Visigoths are the Thervingi who crossed in 376, but there are those who disagree with this idea (and it is entirely possible that it is indeed incorrect as there is no substantial evidence to confirm either possibility). Some historians, such as Guy Halsall, view Alaric's Goths as more of a military force (which they most certainly were in some regards) than as some kind of tribal group. After Alaric's death the Visigoths were settled in Aquitaine as foederati once again in Roman service. From there they would eventually establish their own kingdom that originally included, before a war with the Franks, a large portion of Gaul.

​

The Ostrogoths were most likely those Greuthungi who remained north of the Danube and were subjugated by the Huns. After being conquered this group of Greuthugni is not mentioned of again until the 450s after the death of Attila. After the collapse of the Huns they created their own kingdom and spread into the Balkans. In 488, 12 years after Odoacer had deposed Romulus Augustulus, Emperor Zeno convinced Theoderic the Great to invade Italy, rather than going to war against the Eastern Empire (a conflict that was of Zeno's own making). By 493 the Ostrogoths had defeated Odoacer and established their own kingdom in Italy.

So the Thervingi and Greuthungi Goths were most certainly two distinct groups of people, and, even if the Visigoths were an amalgamation of Thervingi and Greuthungi, the Vesi and Ostrogoths were undoubtedly different groups as well. In his book Barbarian Migrations Guy Halsall actually discusses the importance of noting the distinction between different Germanic peoples, and the problems that come along with lumping them all together in one group. While the Thervingi/Greuthungi and the Vesi/Ostrogoths most likely spoke similar languages and may have had very similar cultures as well, they were most certainly their own individual groups of people. Archaeological evidence, of which I am not as knowledgeable as I would like to be, can also be used to show a further distinction between these groups.

Sources:

Guy Halsall, Barbarian Migrations and the Roman West

Ammianus Marcellinus, The Later Roman Empire