I have had kittens nurse off my mama dog many times. I have also been told of cat rabbit mixes. People where I camp swear they have seen them but I never have and I think it highly unlikely cats and rabbits breed or cats and dogs breed either. Sounds like BS to me.
It's complete B.S.
You can get inter-species hybrids if the number of chromosomes are closish (doesn't have to be exact) --- horse/zebra, horse/donkey, lion/tiger, etc. (and presumably chimp/human, as we are closer genetically than horse/donkey!).
But, as noted above, cats and dogs are worlds apart genetically.
I've heard you can breed a weasel with a lawyer if you tie the weasel up.
A cat and a rabbit genetically couldn't produce any offspring, but whether they would attempt? A cat in heat will try to mate with anything.