There are several Abernathy families of color who have thier 'roots', as it were, in the Giles County TN area, which was one of the places that got a lot of the VA and NC white Abernathy families. I remember talking a few years back with an individual of color at the Franklin TN Family History Center, discussing the interesting fact that we were both looking for the same surname in the same nearby county.
I do know, from certain documents in my family, that one of my ancestors brought a number of slaves to her marriage as part of her dower. Her new husband promptly freed them all. Years later most were still living on the land that had also been part of her dower and had taken her maiden name as their surname.
Careful examination of wills of Abernathy families of NC and/or VA may one day provide the critical clue to identify your as-yet-unknown NC ancestor. Wills of related families, too, should be examined, since many of the daughters of plantation owners brought servants with them to their marriages. I certainly wish you good fortune in your search!