To judge from the lyrics to "From Her Mama (Mama Got Ass)" by Juvenile, it would seem that they believe strongly in the role of genetic differences when accounting for phenotypic differences. The title is misleading, since most of the lyrics refer more to personality and behavior than physical traits.
I stopped paying attention to rap music around 1993, when Snoop Dogg's solo debut Doggystyle proved a major disappointment. I never bothered listening to political or social commentary rap, aside from buying a Grandmaster Flash CD. The Sugarhill Gang got the idea right, and that strand of rap (through Young MC and Sir Mix-a-Lot) finally died out in 1992 when Dr. Dre released The Chronic. I really liked that album at first, actually, and can still sing "Dre Day" and "Ain't Nuthin' but a G Thang" from memory, with pretty good imitation of their voices, I might add. But I was just trying things out, and being more of a charmer than a fighter, I didn't end up liking gangsta rap.
However, I overheard Juvenile's "Back That Ass Up" in college, and it sounded goofy enough to set it apart from thug music, in the same way that "Baby Got Back," er, stood out from the nascent gangsta trend. And of course, music that's only part-rap, like OutKast, I like all right. Still, on the rare occasion when I see what's on rap music TV (usually when some kids in the dining hall tune in to MTV or BET), it still resembles the bad '90s stuff.
I've been meaning to write a post comparing the different types of rap music, based on which reproductive strategies the males follow -- the polygynous sneaky fuckers (Sugarhill Gang, LL Cool J, Andre 3000, etc.), the polygynous harem-guarders (thug / gangsta rap), and essentially no monogamous mate-guarders. It accounts for the differences in the emphasis on displays of dancing skill vs. violence, in how goofy and joking vs. serious and confrontational the attitudes are -- in general, how peacockish vs. gorilla-like they are. Of course, it also accounts for the similarities, such as an emphasis on sleeping with as many women as possible.
As far as I know, when rap music is exported, it's mostly the gangsta strain that infects the population -- almost always a non-African and non-macho culture. South Asian males make horrible gorillas, but are naturally good dancers and jokesters, so it's a shame that they didn't pick up more on the OutKast type of rap. And East Asians just have no business imitating rap music of any kind: they are the monogamous good dads, which is antithetical to rap.
Then there is the social commentary / voice of the oppressed rap, which catches on wherever people realize that they cannot achieve first-world standards of success. What reproductive strategy is that? The loser male, who has no viable strategy but to lash out in envy at those who have bettered him. Yeah, some of the artists themselves are more leader / prophet types, but by and large, those who are really into it -- as well as any political / social commentary sub-genre, like the punk band Crass -- are bitter losers. Lighten up, it's just pop music!