Having and having had rabbit and ducks for over ten years, I would emphatically say NOT to house them together. Ducks are disgustingly messy. I would be very concerned about my rabbits having to live in duck poo all the time. Rabbits get into EVERYTHING. So, if there are things (oyster shells) that they SHOULD NOT EAT, around, they will do something stupid and eat it. They need clean drinking water. I don't use bottles because for one the tubes freeze and two, they can leak. So, I use little bowls for the rabbits, no way would the ducks leave them alone. Then the rabbits would not have clean water.
The hay for the rabbits can be put in small hay feeders, but eating each others grain might be a bad idea. I would do everything in my power if I were you to keep them separated.
That being said. Mine are in the same shed, but divided by a strong wire divider. They have individual play areas. Because the rabbits LOVE to dig, theirs is more secure, so they cannot dig out. But they can run, jump, climb and play in that too. I'd be worried about a dumb rabbit getting themselves in the ducks pool (oh yes they could), but then not getting out easily and getting chilled, etc.
So, all in all, please rethink putting them together.
JMO