Sorry, if no one answer you it's probably because no one has the answer you need. Personnally, when it comes to ear problems I would think ear-mange (not sure it's the name in English?) or ringworm but the photo you posted doesn't look like it. I've never seen anything like that. Look a bit like warts to me, don't know if that's something rabbits can have.
I wouldn't panic as long as your rabbit eats/poops well and doesn't look bothered by it but I would keep an eye an it to check that it doesn't spread. I second trying to find a vet specialized in rabbits so they can give you a definite answer, even if that's not always easy to find (the nearest from me is 1h30 hours of train away, I haven't got a car and I shudder thinking about the next time one of my bunnies becomes sick). But please, if you find out what it is post it here as I really would like to know!