And your evidence for this other than wishful thinking? The facts are that black Republicans pretty much do just as awful as any other Republican in the black community. From Ken Blackwell to Michael Steele to Lynn Swann, the black community flat out does not support black Republicans. They vote Democrat. Period. There is no reason on earth to think Cain would do any better. These people hate pretty much all black conservatives with a passion. Ever heard how blacks talk about Clarence Thomas or Condi Rice on black radio? Listen some time, as another poster said - blacks consider black conservatives to be race traitors.
To be fair, Steele did win 20% of the black vote in Maryland. But too many whites voted for Cardin instead.