If a hanger is very loose I would think that their is a chance of the hanger becoming damaged (from being levered), however no damage would occur to the bolt.
The big overhang route at Legoland has a spinning bolt (it can't be tightened any further) and it appears to be fine and un-bent.
If the nut on the bolt is only finger tight - I don't think there would be any increased risk of the bolt/hanger failing
as long as there is thread above the nut (the thread keeps the nut on, which keeps the hanger there, which keeps your quickdraw attached to the rock, which keeps your rope in place, which keeps you from hitting the deck
