Unfortunately my neighbor had a habit of shooting dogs with a pellet gun... a 5MM Sheridan. He thought he was only "burning" their hide. Somebody retaliated by shooting his dog the same way. A few days later the dog had developed a terrible infection and he had to take the dog to the vet who dug out the pellet. Despite massive antibiotic doses the the dog still died.
Even if the rat shot only barely penetrates the hide the cat is still likely to suffer. As I said bad juju.