I know this is an old thread but I wanted to give everyone an update!
I have had rabbits in with my poultry for ~8 months now and for a while everything was working out very well. The rabbits had their own hutch located inside of the poultry run. See below:
I had a male and female New Zealand White living in the hutch that had a door on the bottom so they could run outside with the birds when they chose to. Everything was going well until my buck reached sexual maturity and began to get very territorial. I had two ducks that liked to go through the bunny door and try and steal bunny food.. well my buck was not happy about that and started going after the ducks .. even when they weren't trying to get into the hutch. My buck attacked and kill one of the ducks and maimed the other - see below:
We have since zip tied the bunny door shut and the rabbits are no longer able to socialize with the birds. It's unfortunate because my doe is very sweet and enjoyed dust bathing with the birds but her mate is just too unpredictable.
My advice would be if you had a more docile rabbit, go for it.. but if you have a rabbit that gets territorial or is aggressive, I'd think twice!