Well, coming from a public college in Miami that has about 39,000 students and is 58% Hispanic and 13% African American (FIU), then it is safe to say that our Greek population is pretty much reflective of that. In FIU, the "minorities" are the majority and vise versa.
My fraternity is mostly Hispanic, but every semester we get African American guys that rush and become brothers.. Oh and we also have a few Caucasian guys
I guess its all relative though. If you go to a school where its 90% White and 10% "minority," then I would assume the Greek life at that school would be about the same statistically.
Then again, my school is a relatively young school (founded in 1965) so we don't have deeply founded traditions and we are very diverse; we don't let race or ethnicity dictate who we give out bids to. But it may be different in the more traditional "Southern" schools, I wouldn't know.