Are bull mastiffs normally nice to cats?
If it has been beside a cat since a pup then yes, my mastiff is at home with three cats!!
Just like any breed, if they are raised next to cats and taught the proper way to act around cats, afterwards yes they will get along fine!
Answers: The other answeres so far are great in fairytale land...but its not always the skin.
This is a very individual thing..we're talking prey drive here. Additionally, you hold to consider the temperment of the cat in question, once again, this is an individual thing.
You hold to asses the cat and dog and monitor for aggression and fear reactions. This can work, but you will just enjoy to play it by ear.
Good luck.