The Haitian Empire's 1805 constitution stated that:

No whiteman of whatever nation he may be, shall put his foot on this territory with the title of master or proprietor, neither shall he in future acquire any property therein.

Only white slaveowners (masters) and colonial administrators (proprietors) were explicitly banned from entering the country, while the more general restriction was on whites owning property.

Various exceptions were clarified in the following article:

The preceding article cannot in the smallest degree affect white woman who have been naturalized Haytians by Government, nor does it extend to children already born, or that may be born of the said women. The Germans and Polanders naturalized by government are also comprized in the dispositions of the present article.

It's important to note that this did not apply to Poles and Germans in general, only to some who were granted citizenship. Additionally, some other whites (such as French widows who had no way to leave) were also naturalised, provided that they renounced any connection to France beforehand.

The reason for Poles being exempted is well documented. Many of the soldiers sent by the French to fight in Haiti were members of the Polish Legion, who had enlisted to help the French fight Austria, Prussia and Russia and restore an independent Poland. They were disillusioned being sent to Haiti and many felt that they and the Haitians shared a common struggle for freedom. As a result, significant numbers defected and fought against the French and these men were granted Haitian citizenship.

The situation with the Germans is less clear-cut. They had been in Haiti since before the revolution. From what I can tell, they lived in self-sustaining settlements and weren't targeted because they didn't own slaves or plantations like the French.

It's interesting to note that the consitution stated that, regardless of skin colour:

the Haytians shall hence forward be known only by the generic appellation of Blacks.

This was intended to avoid retaining any of the colonial hierarchy, which discriminated between varying degrees of "blackness" as well as the more broadly defined races. The Hatians referred to the Poles as "white negroes", which was considered an honour and recognition of their shared struggle.

We generally try not to mod where we post, but curiosity also can get the better of us so I did spend my evening looking into the topic. I was waiting to post it until either tomorrow - if no one else had posted an answer after 24 hours - or else until after someone else had posted a reasonable response already, which thankfully has been the case this evening.

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Unfortunately, what is quite clearly the most thorough source on this matter is Poland’s Caribbean Tragedy: A Study of Polish Legions in the Haitian War of Independence, 1802-1803 by Jan Pachonski, which seems to be out of print, and not available on any sites such as ProQuest or JSTOR. There are several reviews, which offer a taste of what the book has to offer, but while other works do touch on this topic, you would need to track that down to get in-depth coverage of the Polish Legion in Haiti. Still though, there is enough coverage of the topic in other sources to paint a decent enough picture of why some of them stayed.

The 2nd and 3rd Polish Legions were raised by the French from the remnants of the former Polish state, and just oner 5,000 of them were sent to Haiti to attempt and put down the revolutionaries fighting for their freedom there. Thousands of them would die in the undertaking, either from combat or disease, and in the process, those who survived became quite disillusioned with the entire endeavor. Disturbed by the often brutal reprisals committed by the French troops, not to mention the conditions within the army itself which could be quite grim, wracked by yellow fever and stationed in some of the worst extremes of the island. Writing home, many expressed conflicted feelings over having joined for ideas of liberalism, yet now enforcing slavery.

The Haitians themselves recognized that the Poles had quite a tough lot as well. Recognizing their stateless situation, caught as pawns between competing empires, Jean Jacques Dessalines referred to them as “the white negroes of Europe”. Although many of the surviving Poles finished their service and returned to Europe eventually, many in the end chose to defect - as did some Frenchmen, it must be said - and throw their lot in with the Haitians, in the end numbering several hundred of the Polish force. With the end of the war, and Haitian independence, the new government recognized the contribution of the Polish defectors and granted them citizenship. Similar protections were made for white women in the country who were married to black men, as well as their ‘mixed-race’ children.

An exception was also made for some Germans, although there is less to be said about them. Some of the naturalized Germans may likewise have been defectors from the multinational force the French had sent, but most of those referenced by the provision were members of a small population of Germans who had settled on the island prior to the war for independence, and wisely had stayed on the better side of the Haitian rebels, so allowed to stay.

Importantly, with their independence, Haiti considered it important to secure their identity as black. Article 14 of the Constitution made this quite explicit in stating that:

All acception of colour among the children of one and the same family, of whom the chief magistrate is the father, being necessarily to cease, the Haytians shall hence forward be known only by the generic appellation of Blacks.

Even those citizens who were plainly considered white by most understandings of the term were thus legally black insofar as the law of the land was concerned. They may have been granted citizenship, but their presence had to be subsumed within the Haitian self-image as a ‘symbol of black power’.

Sources

Buckley, Roger Norman, Pachonski, Jan, and Wilson, Reuel K. “Poland’s Caribbean Tragedy: A Study of Polish Legions in the Haitian War of Independence, 1802-1803.” The American Historical Review, December 1987.

Dapía, Silvia G. "The Polish Presence in Latin America: An Introduction." Polish American Studies 69, no. 1 (2012): 5-8.

Dubois, Laurent. Avengers of the New World: The Story of the Haitian Revolution. United Kingdom: Harvard University Press, 2009.

Nicholls, David. From Dessalines to Duvalier: Race, Colour, and National Independence in Haiti. Rutgers University Press, 1996.

Santiago, Charles R. Venator. "Race, the East, and the Haitian Revolutionary Ideology: Rethinking the Role of Race in the 1844 Separation of the Eastern Part of Haiti." Journal of Haitian Studies 10, no. 1 (2004): 103-19.