I'm impressed by all the civil conversation and excellent points made in this thread.
Since joining GC and learning first about the NPHC (I had never heard of these organizations before) and then about the debates surrounding this very topic, I have often times felt bad that my chapter is not more "diverse". However, my campus lacks racial diversity of any sort - there are perhaps 10 African-American students, and a handful of Hispanic or Asian-American students. We just don't have a lot of racial diversity, period. This is by no means a fault or downfall of my school, just a fact. Hence, all of our Greek houses are lacking in traditional racial diversity - for the most part, we're just a bunch of "white kids". I would hope, however, that minority students who were interested in Greek life would feel comfortable and welcome at our recruitment and COB events.
Racial diversity within our chapter is not something which we have given much thought to, and I'm sure that if an African-American, Hispanic, or Asian-American woman went through recruitment, we would give no pause to the color of her skin, but view her as we would any other PNM. One of our seniors who graduated last year was Mexican-American, and always joked about how she stuck out in our composite... However, I think the only reason she really stuck out is because she was drop-dead gorgeous.
Due to our campus' visible lack in racial diversity, our chapters strive to gain a membership that is as diverse as possible in other ways - students involved in different campus groups, with diverse interests and talents, who come from all different backgrounds. In my mind, this sort of diversity - and I would, without hesitation, say that our houses are more than diverse in this manner - is certainly as important as having a racially diverse house.
Hope my post doesn't offend anyone.
And my two cents on the actual question at hand (since my post is a bit of a hijack) is pretty much what everyone else has been saying. Humans nauturally gravitate toward their "comfort zone" and seek to belong to groups in which they feel most comfortable, and this rule certainly applies to selection of a GLO. If I were, say, an African-American woman, I could certainly see myself being attracted to an NPHC group or an multicultural GLO if that is where I felt the most comfortable.