Santorum campaigned for and traveled with Romney during the primary season of '08. When Romney made an appearance in St. Louis at that time, I went to hear what he had to say, since I wasn't crazy about McCain, and my man Thompson had just dropped out. My reservations about Romney were specifically about the abortion question. I knew of Santorum's reputation for being solidly pro-life, so I pulled him aside and had a conversation with him about Romney's reported "conversion" to the pro-life side. Santorum assured me that he thought it was the real deal. So at that time, at least, Santorum was OK--more than OK--with Romney. Whether Santorum is still OK with Romney--enough so that he would run with him as his VP--I don't know.
I think Santorum would jump at the chance to be VP. He’s young, if things went well, he can run for Prez next go ‘round that available.
I don’t think his differences with Romney would be a deal-breaker. Just my take on it on this point.
Romney needs a solid guy like Santorum as his running mate. Even though Rick’s from PA, he’s more like a tapping someone from the South in terms of his style and appeal, balancing the ticket thing.