It's totally normal. For some rabbits it's more impressive than for others... The best way to remove a lot of dead hair from the source without the rabbit kicking a fuss is simply to get your hands a bit moist and to pet your rabbit. I do it while my rabbits eat their vegetables and it works like a charm (a brush getting near their rear ends will cause an immediate rebellion). Hair shouldn't cause any problems as long as the rabbit eats his hay. Hair balls only appears when your rabbit's guts are already slow, hair doesn't cause GI stasis by itself, so there is really no need to worry - even if, of course, an eye should be kept on the litterbox at all time ^^.