sure — I believe that some black people will vote for Herman Cain because he’s black. No doubt.
Voting for someone who is in your demographic is common — thinking that a person who shares your life experience will make decisions similar to yours is reasonable.
But voting for Herman Cain because you are both black is like a Republican voting for any of current primary candidates merely because they have an R after their name.
I don’t believe the either voting strategy will come out as your expect.