Is that different from Cockney?
That's an interesting observation. In Michael Crichton's excellent book "The Great Train Robbery" he explores at some length the London slang of the criminal class. They used this jargon, and it's quite elaborate, to determine bona fides. If one couldn't keep up w/ the dialog then they were clearly an impostor.
I suspect that ebonics works in a similar fashion being used to seperate genuine ghetto from wanna be ghetto.