I don't know the answer, only that in general the 'legume' (pea) family of plants are not advised as food for rabbits because of their high starch content.
I don't think the odd one that gets through will do much harm, - vetch (if that is what they are,) grows wild, so I guess the odd wild bunny will nibble on them.
My bunnies seem to eat everything plantlife that doesn't move to no ill effect. The only thing they won't touch that grow in my garden, are snowdrops! Perhaps they have some good idea what is not safe to eat.
Hopefully someone with a more definitive answer will come along.