I'd probably throw up in my shoes if I heard it, much like I did when I heard P Diddy's blasphemy of Kashmir for the Godzilla soundtrack, of course, Pagey was on board for that one. I do like some rap and do think there are some great crossovers out there such as the Run DMC/Aerosmith collaboration (can't deny that exposure really re-jump started Aerosmith's career), Anthrax/Public Enemy doing Bring Tha Noize, The Beastie Boys crossover alot rap/rock/punk/funk (Licensed is a great album, Check Your Head really stepped it up a notch), the Judgment Night soundtrack brought some very interesting collaborations of rap/rock together, Ice T's controversial band Body Count had some cool stuff, there some elements of rap in Rage Against the Machine, and love em or hate them, bands like Limp Bizkit, Incubus, Sugar Ray, Linkin Park all mixing in somebody scratching away at a turntable, and of course good old Kid Rock and my personal fave 311.
I guess I don't mind it when rappers/rockers get together and create something new together or get together to revitalize something but I guess I'm not a big fan of a rapper taking his/her own direction with something like Crazy Train and kill a masterpiece. But then again, I always did like the Jamie's Cryin' hook that Tone Loc sampled on Wild Thing!!!