both my bnl and i keep rabbits and chickens in the same area, in fact helps with all the rabbit manure, the chickens scratch and turn it over very often, helps alot with the ammonia smell that will build up if just left alone, not to mention keeps the flys under control also d/t the manure staying drier. however, we have had 2 problems occur over the years. my first hutches were too low to the ground, and the chickens would peck the toes of the young ones, the other is that if the chickens can get on top of the hutches (we use the wire cages), they poop all over the rabbits, and it really makes the does nervous, some have aborted or abandoned litters or have been very difficult to breed. just keep these in mind and you shouldn't have any trouble. in fact after we worked out our 2 problems, everyone seems happy, and are co-existing well. this has been over an 11 year period combined.
good luck,
dave