The USA Today poll is just about the primary. The poll does NOT suggest that the disaffected 20% is really going to vote for Hillary, as it were, in the General. That question was not asked. It was about the primary. Polls show Rudy even or beating the Dems in the General, in a very negative environment right now. Romney is getting slaughtered at the moment in General Election matchups, and McCain is slowly sinking, as he loses his moderate swing voter attraction over various matters.
Rudy will not win the Republican primary without solid 70+ acceptability to Republican voters. He does not have it now and as the campaign moves along it will most likely diminish as he is forced to address his positions and his views become better known. In February of 1999 Bush had an 80% favorability rating among Republican voters.