And, IMO, this is the crux of the matter regarding Eminem. The fact is that he's more successful than other hip hop artists BECAUSE of his race.
Want proof? Today I heard his new single on the radio. It was on KNRK, the local "alternative" station. Guess how often black hip hop artists have been played on this station? Something in the area of NEVER. Does getting played on a popular radio station make you more successful? Well, I doubt it hurts.
Fact is there are boundaries set up that work against black artists, and just how racist these constructs are is often illustrated in the cases of white hip hop artists like Em, Beasties, Vanilla Ice, etc., and how they're treated by radio, tv, and the rest of the media. I've never heard anyone say Eminem is to blame for the institutional racism that exists within the music industry, but is he benefiting from it? I think that much is obvious.