Jazz music does attract a relatively high African-American audience. A 1992 report by the National Endowment for the Arts found that while only 12% of Americans are African-American, they represented about 19% of jazz radio listening. I saw a report newer than 1992 at one point, but I don't have it handy to reference right now. It also suggested that jazz listeners oversampled blacks. Certainly moreso than classical.
However, I very much agree with BigA that is going to be an old audience. Not a lot of 30 year olds of any ethnicity who are looking for Alphonse Mouzon records.
What about him? Just because he is a minority and under 50 doesn't mean much by itself. If you weren't listening to Diane Rehm, would you even know that "1A" exists? Also, "1A" doesn't even air in several of the major markets where so many minorities live. Chicago, Atlanta, Miami, to name a few.