I don;t think it's the same for rabbits at all - cats are meat-eaters by nature, bunnies are plant-eaters, so I imagine their nutrritional needs are completely different.

Miss Hoppy will eat choice pieces of grass, but we'd have to have a whole herd of bunnies to replace the lawn moser - she's very picky! (And has never gotten sick after eating anything she found outdoors, either.