How's he on Foreign Policy?
That's the wild card. As with any governor he has no foreign policy experience himself, but there's nothing in his resume that suggests he'd be anything but a hawk. I'd assume he'd be as effective as Dubya on the WOT, since Bush also came in with no experience, but put together the right Administration and the rest is history. If Sanford either picked a VP like Cheney who has the experience, or a good cabinet, I think he'd be fine.
Actually, Condi Rice might make a good Veep for Sanford. She's not as conservative, but he'd be the decision maker, and she could help with foreign policy!