Are you looking at Keyes from the standpoint of bringing in the black vote? If so, do you think the black vote is crucial to Trump or Cruz winning? I think perhaps looking at the probability of who the opposition is going to pick and try to offset that would be more prudent. I don't think Hillary will pick someone Black to run with her, I believe she will pick a Hispanic such as Julian Castro to offset Cruz or Rubio or she may pick Warren to pick up the more progressive left voters.
BTW Trump has mentioned that he would pick Cruz as VP. I am sure Cruz has already selected who he would pick and I not only think they will be surprising but an unbeatable team.