In economically poor black neighborhoods there are always more than a few poor whites that live in these neighborhoods as well. They're greatly in the minority, but they're there. Even in the late 80's and the 90's you had a few white Crips. Only natural there'll be white GD's, VL's or Stones as well. It's a case of maybe one out of five hundred, but it'll happen.

For instance, when you take a look at the Eazy-E video of "Real Muthaphuckkin G's" near the end you can see one or two white guys as well. Probably childhood friends of other people in the video.
I saw a Lord Jamar interview where he told that during the Latin Quarter days in 80's NYC you had the white rapper MC Serch who was at the time often the only white guy attending underground hip hop events among hundreds of African Americans and Puerto Ricans.

You're around the people you grow up with, it's simple as that.