Has he ever physically hurt one of the cats? Is the cat trying to get away or does he lay there and wait for the attack? My experience with cats is generally, if they don't want the attention from the dogs, they will avoid them all together. Cats will put up with an incredible amount of rough play before they let the dog know it's too much. With small dogs, I would worry about scratches to the eye, but if the cat is instigating the play, like sitting under a table, slowly waving his tail from side to side, crouching down, while staring the dog down before they pounce on one another, it sound like mutual play to me. However with that many cats in the house, I have seen where dogs will be more aggressive towards one cat all while being best friends with another. Each cat has an individual personality and some will put up with a lot more than others, and some personalities clash with others just like with people.....
