These days, it is somewhat pointless to truly define a genre of music. The only difference is the voice of the performer. Some genres are clearly defined, others are evolving. It all depends on the performer. Jazz, for instance is evolving into many different styles(compositions, arrangements, vocal and instrumental approaches). Hip-Hop is no exception. Like blues, rock, classical, country/ western, bluegrass and gospel, it is about the music that is new, yet familiar to most fans. Hip Hop was established as a "urban" creation that enjoyed an underground success in the black and Latin/Hispanic communities when it came out in the late 1970's. And when it came out into the mainstream, thanks to the group Blondie, led by Debra Harry, she gave rap the spotlight with the song Rapture and it had an adventurous and otherworldly vibe(it's influential tone and beats were heard in many hardcore and softcore porno films). I am surprised none of these guys ever gave thanks to Blondie for helping them get through. Eminem, pretty much lived and participated in the rap/hip hop genre, thus establishing himself there. In the final analysis, it isn't about the race of the performer, it is about the music. Sure, some genres like country/western and bluegrass remain true to the music and the spirit and traditions of those that came before. Now, things have opened up for people of all races and ethnicities in the music industry. So, it is fair to say that no one, established or not, has any say as to who is genuine. That is for the fans to decide.