I think these are two very different things. I guess a bigot will always see negative things in people of different background, no matter how "careful" or "careless" they are. But that is altogether different from somebody deliberately espousing the worst stereotypes for public entertainment or consumption.
Self-depreciation seems to be a tactic deliberately exploited by racists of various stripes. A few years ago I attended a presentation by a known racist on JHU faculty (his name was Gordon and I am not sure if he is still with jhu) showing the results of his study (funded by the Pioneer Fund) supporting the "Bell Curve" claims. His assitant (the guy who flipped his slides and distributed handouts) was a Black guy. I am pretty sure that his participation in that openly racist event was a deliberate tactic to make it appear less racist than it was - a message of a sort "even some Blacks accept my findings, so it is not as racist as you may think." The same thing seems to be at work in the gangsta rap industry.
I read somewhere (forgot the source) that when rap first came out in 1980s, black stations refused to play it, but white stations (mostly college) picked it up. Seems to be the same trick as the tsarist or nazi propaganda machines publishing the Protocols of the Eders of Zion as supposedly 'authentic' Jewish source.
Wojtek