Really? I think they'd have several issues to give their relationship tension. First off, his "furry little problem"- you know he'd have more of a problem with that than her. In the same vein is the age difference, with which he would again take more issue. On Hermione's side, I'd have to say that since she's never spent time with an intellectual equal as a social equal, she'd definitely have a very hard time with that. And I think that they each have any number of little traits that would bug the other to no end.

But not every relationship is about tension and contrast. Some people are very similar, and do well in relationships because of that degree of similarity that some might find absurd. Relationships don't have to be hard, and I think these two characters need something easy after all they've been through.

Of course, making them accept that it really is that easy would be a good source of conflict between the two.