Unless you have had issues in the past with either the chickens or rabbits becoming aggressive, you should have no issues with housing chickens and rabbits together. There are many reasons why they are compatible house friends and will work together in a run outdoors.
Chicken are able to make a lot more noise than rabbits, this is a defence mechanism which keep them safe from foxes and other predators. The chickens should cluck and will be able to alert you. Housing them together may also save your rabbits which is a good reason to keep them both housed together.
The reasons that they are compatible mainly come down to what kind of animal they both are. They do share a lot of qualities. They both eat the same kind of food, they both need letting out in the daytime for exercise and they are also both as vulnerable as the other when it comes to other animals.
If the animals eat the wrong food, nothing will come of this and it should have no negative effects, unless one of the animals is on medication, in which case you should separate them. They will also both want to get let out of the cage or run frequently, this means that they will get enough time apart from each other.
You just need to make sure that the animals have enough space to move around and will not get in each others' way. They may take the stress of cramped conditions out on each other, but as they are both very non-confrontational animals, this is unlikely unless they are under stressed circumstances.
I kept adult rabbits and adult chickens (including one rooster) in the same area (total, about 12' by 10'). The chickens were allowed to leave the pen during the day if they wished (only a 3' fence) but they usually stayed on their "side". The rabbits had made burrows in the ground that allowed them to separate themselves from the chickens if they wished. Their separate area was about 4' by 5'. (the two species were originally separate, but with the burrows they ended up mixing). The rooster pecked each new rabbit squarely between the eyes once. I suppose it was his way of marking "his" rabbits. After that initial mark (as baby bunnies) they never harassed each other again. If the chickens didn't get back to the cage at night, the rooster would put his hens up in some small trees.
The chickens scratched and turned over the top 2" of dirt, and the rabbits burrowed and turned over the top 2' of dirt, in select areas. When we cut fruit tree branches, both species worked together to strip down the branches to kindling. They "processed" leaves, lawn clippings, and other yard debris as well.
I fed the rabbits (from late fall to early spring) rabbit pellets. The chickens got egg-layer feed year round. Sometimes the rabbits would get into the chicken feed (a sign they needed their own food, or additional grain supplements), and both used the same clean water and salt mineral block.
I sometimes found does sleeping in the chicken nests, unless there was a broody hen. Baby bunnies and chicks would often sleep in one giant pile of fur and feathers.
This arrangement lasted for about 3 years. Peak rabbit population (36 - does and babies), peak chicken population 10 (8 hens, 1 rooster, 1 jr rooster-soon-to-be-"and dumplins")
The rabbits were meat rabbits for family consumption, and we often gave away the extra eggs.
I never had a problem, and the only time I lost livestock was when the rooster was ill (and caged separately) and I lost an entire litter of bunnies to a hawk. So I'm guessing the rooster protected the rabbits.
It is important to note that none of these animals were "caged" - they were able to roam within the areas, and I suppose if they'd wanted to get out, they could easily have done so. So they must have been pretty happy together.
I have 9 hens and 2 roosters that all live together with my rabbits. The hen coop is at the seperate end of my garden to my rabbit hutch, though. At first the chickens didn't like the rabbits being near them at all, they'd puff their feathers up and jump about, and one of the hens used to peck the rabbits, not hard enough to annoy the rabbit though. After a couple months they're completely used to eachother. My male rabbit sometimes chases the chickens for fun, but there's no violence anymore. The hens do get bothered if the rabbits go in their egg box sometimes, but they don't mind them being in the coop, and the chickens sometimes make their way into the rabbit hutch. The only problem I would say is that you should get any male rabbits neutured as yes, they will mount your chickens.
Rabbits and chickens can be raised in the same building. But should be kept completely separate. Not because of there behavior,but because of the possibility of chickens passing on disease to the rabbits. Chickens carry salmonella and bird flu. Which any bird person should be aware of. Rabbits are much more susceptible to disease of this type. If your flock is in good health, in theory there should be no problem. Your just taking an unnecessary risk.this is more of a problem in winter when they're cooped up in close quarters
I have 3 chickens and 2 rabbits that share a small paddock. (They all have their own houses that they can go into when they want and are locked up at night). They are happy to share the outside space peacefully but chooks don't like the bunnies going in the hen house! But then the bunnies have now know not to go in. The chicks have only ever flapped at them and neither party has ever been aggressive. I thinks it only works out okay as they do have a reasonable size space to run around in and have their own beds.
I have 1 chicken, 1 male rabbit, 1 female rabbit, 2 guinea pigs all in an area of about 5metres by 3metres. The female rabbit has babies in a little hutch which the door is permanently open. The chicken sleeps on the floor in the hay next to the male rabbit with its head ret on the rabbit! The male rabbit humps my chicken. My chicken peks the guinea pigs.. They are new, the chicken came after the rabbits.
I have a cat and a rabbit and a duck all in the same house but I have herd that chickens can be dangerously aggressive and territorial some properly could live with a rabbit. It all depends on age if the chicken is young it my work put them in a cage with a separate this way they can smell each other decide for them selfs if they wish to get along (and if they don't they can't harmone anouther) watch them and it wont be hard to tell weather there is a chance it will work. If you see that it may work still be cautious and keep an eye on them they are after all animals (this makes them wild and unpredictable). Make sure you feed them separated and give them plenty of space :)
As with everything else it depends on your animals personality type. A rooster is aggressive and it probably wouldn't be a good idea. I have 4 hens that have been raised by hand and a rabbit that is a house rabbit but prefers to be outdoors during the day. They get along just fine. If you are worried about it being sanitary then add wood shavings and clean your coop regularly - you should be doing that anyhow.