Can a rabbit and a Cat mate?

depends wich 1 is the male

I had a buck that mounted a female ferret and I've seen a picture of a buck rabbit on a hen. Mounting a cat wouldn't surprise me.

Any male animal will mount anything of suitable and sometimes unsuitable size. If you are asking whether they can produce offspring the answer is definitely NO. They are two different species - it is genetically impossible. So called "Cabbits" are simply deformed cats - usually manx. Think about it - cats are carnivores - rabbits are herbivores.