I believe that my chapter, Mu Alpha, is a very diverse chapter. For whatever reason, my chapter attracts people of all types of backgrounds. And because prospectives see people who look like themselves, they feel more welcome during the rush period. I don't know how we do it, I don't know how we maintain it -- but somehow it works.
I think APO on the national level is doing pretty well -- or at least they were when I was at the height of my undergrad activity. At the Philly 2000 convention there were brothers from EVERYWHERE!!!! And the strange thing was that even though we looked different, we had many similar chapter traditions.
I think that in essence, our principles are for everyone, so we naturally attract a wide variety of people. If a chapter attracts only one type of person, it will be hard to atract different types of people. Every once in a while, you might have that one random person who stumbles upon APO and loves it, but is different from the rest of the members. That brother should be encouraged, his leadership abilities fostered, and helped in any way possible when it comes to recruitment.
Sorry I couldn't find anything to really be critical about when it comes to diversity.