St. Marron, a folk saint unique to New Orleans, was the patron of runaway slaves; the name derives from the French word marron, meaning a runaway. He was usually represented by an image of St. Anthony, apparently this saint not only found lost people, he aided those who “got lost” on purpose.
-Carolyn Morrow Long, A New Orleans Voudou Priestess: The Legend and Reality of Marie Laveau
Reditus 
In the main, St. Marron was considered to be a distinct person… however, as is very often the case in Voudou, the two had several attributes in common and there was a certain amount of “crossover effect” in the hearts and minds of some of the practitioners. Since the African beliefs were originally proscribed by various of the ecclesiastical authorities in early times, St. Anthony was resorted to as a sort of camouflage substitute for Marron– this enabled the practitioners to disguise the true nature of their veneration.
As such, it is very much the same with Papa Legba/St. Peter, and also as with Papa Legba/St. Lazarus. Most of the other Voudou lwa likewise have their own counterparts among various of the Catholic saints, but the correlation is not always quite so evident, precise, or well met as some might think it would be.
Leah: St. Marron still has a very few serviteurs among the Voudou laity in the US, but he seems to be gradually fading away– probably for the very reason you cited. As such, these days St. Marron mainly serves as a patron to those who feel oppressed by the secular government more than anything else.
It is much the same with the ship of Erzulie Dantor, and in fact Marie Laveau often serves as a substitute for Erzulie in these days and times. This is especially true of some of the Voodooienne of the Southeastern US, especially in Louisiana and New Orleans.
Hope this helps!
Interesting. Was he considered at the time as a distinct person, or just another name for St. Anthony?
Is there still devotion to St. Marron in New Orleans, or did his cult end with the disappearance of slavery? My Google search isn’t turning up much…