I don't think it's so much that audiophiles "hate" rap/hip hop (and punk, and grindcore, etc.) so much as that they listen to music for reasons that don't mesh with those genres.
Those genres tend to be heavily bound to youth subcultures, so things like recording quality and subtle composition tend to go out the window in favor of fitting into a clique and maximizing sonic shock factor. There's also generally an age gap between the average rap/punk/etc. scene and the typical person able to afford true audiophile grade gear. Generalizations? Yes, but still true in 99% of cases.
Of course some of the acts in those genres do defy the stereotypes, but you can't expect people to go searching for them for no particular reason when they're effectively a needle in a haystack. Yep, most people think rap/hip hop and think - Snoop Dogg, 40s, pimps and hos. They're wrong of course. You can find "rap" from late '70s Germany when the nerds programming early synthesizers didn't know how to sing so just "rapped" over their melodies. I don't think it's the public's fault, though, that "rappers" themselves have gone out of their way to reinforce the narrowest stereotypes possible.
However, as I've mentioned before, my definition of audiophile seems to differ from many on this board; FiiO + ATH-M50s is not "audiophile". Audiophile traditionally doesn't mean just finding something satisfactory/industry-standard/currently-in-vogue to gain access to your music. It's more like savoring the subtle and often admittedly ridiculous nuances between different mediums. In ways it's a guilty pleasure, but one of the most healthy ones I can think of.
I'm much more of an audiophile when it comes to non-headphone audio gear. I'm still relatively new to "high end" headphones, and until this year owned nothing but a pair of Grados and a pair of Sonys, with no amp. Every time I consider taking the plunge into one of the $X,XXX+ models with a serious signal chain behind it, some preamp or towers or acoustic treatment or car audio thing sidetracks me. Perhaps it's a matter of time, though.
