My flemish giant (see other post for pics) tolerates some chickens. But, she doesn't tolerate roos. She gives them a warning growl, then she thumps her feet...She's likely to put a hole in the floor!!
The key is to put the rabbit with the chickens, not the chickens with the rabbit. Bunnies are very territorial...Just like when you breed you put the doe with the buck...Does are much more territorial, but bucks don't tolerate other males (haven't had any experience with putting bucks with chickens)
Be aware that there may be sqwables (sp?) because they're new to each other. I would watch your hens, as my Silkie hen is MEAN to my bunnies. She will literally attack my holland and mini lop rabbits. My flemish fares so well because she's huge.
MAKE SURE YOU WATCH THEM AT ALL TIMES!! Either the chicken or the rabbit might freak and attack the other!