We don't know the details of Rand's half-hour conversation with Romney. We don't know what, if anything, was offered. Or whether Romney offered anything to Ron Paul, they do talk on the phone and they and the wives have been very friendly throughout the campaign.
I do agree that it was a little offensive for Rand to make that endorsement on Vannity's show. He's insufferable and has been cruel to Ron many times, especially in 2008. But I recall that Ron Paul also made his own announcement of his 2012 run also on Vannity's show, the last time he appeared there, I think.
But O'Reilly probably wouldn't have carried it and Greta doesn't have enough viewers. The best would have been their real friend, Cavuto, but an afternoon announcement wouldn't have the impact. So Rand had to play his card as best he could, despite Vannity's smirking and catcalling and tiresome repetition of pet phrases for his dull-witted Neanderthal audience.