Since no scores are kept, and there's nothing to "win," I don't see what difference it really makes, but rules are rules. It's a pretty low-key event, with lots of camaraderie and fun. Put together a few broadheads and if those get lost or broken, which is likely, I doubt that anyone would call you on it if you finish out the round with field points. There may be some scored events apart from the general course, and of course you would have to follow the rules for those particular events.
Actually, most of us look forward to shooting broadheads at 3D targets, since there isn't much opportunity to do that otherwise.