I'd say no, your rabbit doesn't need one provided you feed a good diet, ie, 80-90% hay along with an eggcupfull of good quality, high fibre pellets (which will have all the vitamins and minerals he needs) and a little veg/wild food selection (see our foraging 2011 thread for bunny safe ideas).
Should you find you need to make any adjustments to your buns diet do so very gradually, 1 change/new food at a time over a 2 week period. Don't make any changes until he is settled in the home (say at least 2 weeks if he's new to you) and best not to intoduce veg if he hasn't had them already until he is about 12 weeks I think.