A rabbit peeing over himself would kinda catch my attention. Not in the 'OMG, vet now!' way a rabbit not eating would, but I would keep a close eye on him and take him to the vet if it does occur again or if you see any sign of irritated skin / ugly fur around the tail. It might be the sign that something is preventing the rabbit to clean himself up properly or of a urinary problem.
I agree that your rabbit will probably wash himself up.
Just in case he doesn't, I've got a pig-rabbit who doesn't pee on himself but who washes himself very quickly and not carefully at all (I've had him at 8 weeks and he's been like that for the past 4 years, so it's not a health issue... washing himself just doesn't interest him and I swear I saw his bunny friend sniff him, make a disgusted face and wash his feet a few times). It's not a very big problem but his under paws tend to get matted and this moron had pododermatitis once because of it. So when it looks dirty I do wash his back paws. I do that with a basin containing about two cm of warm water that I put on the floor. I sit in front of it and hold the rabbit so that only the dirty places get wet, just dipping his tail and paws quickly. Then I use a small dollop of special shampoo for rabbits (you can probably find that at the vet - I honestly can't tell you if it's just a marketing thing or if this shampoo is really 'special' but better safe than sorry), just washing the back paws and rinse. Afterwards I use a towel and paper towels to dry him. I only do this if it's necessary and never when the weather is cold. I generally end up more wet than he is. If your rabbit is disgusting and smells bad, I probably would wash him if he doesn't get to it. Sometimes, rabbits are weird. After her spay, Aki (who has always been a very clean rabbit) wouldn't touch her hindquarter at all and got really disgusting. After a few weeks, at the end of my rope, I finally washed her. She hated it and immediately began licking herself to get rid of the smell of the shampoo and the remaining moisture after I did and, like magic, she was cleaning herself up again after that.
