GMs hire who they think will lead their team. The best possible candidate for them. Too bad there are more Rahim Morris's and singletarys than Tomlins and fraziers. There's a reason Fewell doesn't get hired and its not his color.
There's not enough of them not because they are being smothered by the white man. It's cause there's not many that even want to get into coaching. Trying to say black GMs won't hire a black guy cause he's in a room full of whites is asinine. He's not worried about losing his job cause he hired the wrong color, he's worried about losing his job cause he hired the wrong coach.