I totally plead ignorant on this one, but wanted to give someone a glimpse of what being in a greek organization at a southern school can do to you!
I was an AOII at Georgia Southern University my freshman year. As far as I can remember, there were no african-american girls going through rush, though there were some of other ethnicities. However, the african-american sororities at GSU are pretty big, so I doubt any of them felt compelled to go through rush in the historically white sororities.
Then I transferred to Oglethorpe University, a small D3 liberal arts school. One of my first days on campus I went to a meeting about cheerleading because I was thinking about trying out. Well, at the meeting there were two african-american girls and I noticed they had Chi O lavaliers on. I can honestly say that my first reaction was shock because there were no african-american girls in any of the historically white sororities at GSU. I later learned that 2 of the 3 sororities at OU had a significant african-american membership (in part because there are no historically african-american greek orgs at OU). Now I no longer consider it anything out of the norm, but gosh was it a shock at first!