Social conservatives speaking during prime time: President George W. Bush, Vice-President Dick Cheney, Lynne Cheney (she's a social conservative on almost every issue, FMA notwithstanding), Senator Zell Miller.
Social moderates speaking during prime time: Rudy Guiliani, Arnold Schwarzenegger, George Pataki.
Sometimes conservative, sometimes maverick, sometimes moderates speaking during prime time: John McCain.
The full line-up of speakers hasn't been made public yet. Bloomberg isn't speaking during prime time, he's speaking during the day. Guiliana, McCain, and Schwarzenegger are three of the most popular and high name recognition Republicans in the country. The only one I'd drop from the line-up is Pataki (I'd give him a non-prime time slot). Given the mix, and the fact that there's still one prime time slot open (which will likely go to a conservative), I don't see the problem.