A lot of guys seems to think that girls love it when they rub all over them when they're dancing. If the guy doesn't have as much experience - dating or otherwise - he could just not have had a girlfriend who explained to him that just because he likes to rub his goodies on a girl's leg doesn't mean the girl's all about it. Or, he could be really horny from his lack of experience and be a little too excited about the prospect of even dancing with a girl. Chances are, it's probably both.
I've known a lot of shy guys that do that when they're drunk just because they really want some lovin' but are too shy to do anything normally and would never think of trying to REALLY get all over girls they're interested in, even when they're wasted. So, if all the guy does when drunk is dance a little....overzealously, if you will...at least he's not one of the guys who shoves your hand down his pants.
I wouldn't freak out about it, and I think you'd have a chance with the guy. He'd probably need some coaching on girls in many ways, but I'm guessing if you were in a relationship, not only would he never hump anyone's leg but yours, he'd probably calm down on the dance floor when he got some real lovin'.