I don't agree that asking this question is taking the humble route. Asking if they have any concerns doesn't mean you think that they should. In fact there's an obvious subtext that if they do have concerns then you can address them, so they're not really valid. That's almost the opposite of being humble!

Personally I don't think it sounds either arrogant or humble overall, plus it shows a willingness to discuss difficult things in a polite manner (at least the question as stated above was polite) which is also a plus for a candidate.