When the kids and the cat are running to the cemetery they come to a closed (but not locked gate), the cat appears to jump through the bars, however the bars are much to close together for the cat to jump through them. So is the cat a ghost?
cats can squeeze into such small spaces that it's impossible to think of it, it's a normal cat thing, not a magical cat thing. they are also expert jumpers, and i think if you had been in the body of a cat for 300 years you'd know how to jump. the cat wasn't given extra powers, just immortality. the witches didn't want him to ENJOY his time as a cat. besides if the cat can get run over, i don't think it's a ghost...and in movies, ghosts are generally transparent (didn't you see the end?)
The cat can fit to any shape, like when he got hit by the car and just got flattened out...If it were true that he could only, not die, then, he wouldn't have been flat and poufed back up, he would have just been seen as normal when he got hit by the car.