Well, in one dojo I trained at regularly there were about 3 of us in 8 years or so, two of us stuck.
In another dojo, it is fed from Temple University in North Phila. (the instructor teaches Aikido for the university and is on staff there), so there is a good source of African American students there. Also, when this instructor first started some 30 years ago, he didn't have the dojo he has now...and it certainly wasn't in the same type of neighborhood...
I don't believe either instructor made or makes a point of 'recruiting' African Americans. Because of the demographics where the dojo is located, you see a good mix of people...some male, some female, some black, some white, some yellow (more or less on the colors). The point is, everyone gets treated the same...there isn't one test for me and another for someone else based on race. I guess gender can be a little trickier with testing...but I know the 3rd dan who is a woman is tough as nails, and has very soft feeling but effective technique. I don't feel like she is doing a poor women's imitation of men doing aikido...she is quite outstanding in her own right.