Steve,
Jud and I spoke about this the other day and he thought young greens did quite well on chicks alone. I think it would be alright for the first year or two, but it would probably be good to supplement greens older than this with an occasional rat, or switch over completely to rats. As they get larger, you are going top be needing to feed rabbits, as adult chickens probably would not have the food mass necessary for an adult green unless you were feeding quite a few of them.

Kelly