The only ones who won't vote for Guiliani if he is the nominee are the Irreconcilables who don't like anyone much. They are closer to 6% than 30%. And that 6% would be offset by 10-20% Democrats and 2/3s of the Independents. Guiliani would approach landslide numbers against Hillary.
Sadly, it would probably take another 9-11 to put him ahead. I think he would be a great asset to anyone a little closer to the Senate, but I just don't see Rudy accepting the #2 spot.