This is pretty interesting, though I have no idea what an "oicotype" is:
http://www.pantheon.org/articles/s/snallygaster.html

Here's a mention of the slave aspect, sort of: In one legend, the Snally Gaster is a thing immigrating from Europe which eats African Americans. In another, it is a champion of ex-slaves and their families protecting from and interfering the hunters.
http://www.math.buffalo.edu/~sww/snally-gaster-CONTACT.html