Someone might have a good answer to this question if you could provide the diameter of the superball and the size of the beardie.
Also, not all beardies are into playing with balls, so if you do determine that the size is safe for him, don't be too disappointed if he doesn't relate to it. We got a ball for our beardie once -- no reaction. :|
If the dragon can get it in the mouth , it may not be able to swallow it , or it might, and if it did swallow it I'd be getting the dragon IMMEDIATELY to a reptile vet - it will not be digestable and impossible to pass and would be life threatening situation.
I remember them from the mid 60s when I was a kid, I think they were about 1 inch in diameter. So definitely a hazard for any beardie over 200g.
I'd not use any ball that they can bite into and eat pieces of, like rubber superballs or anything foam...Chunks of rubber will certainly cause an emergency.
As I recall, "superballs" are made of pretty hard rubber (or whatever synthetic material it is), and I doubt if a beardie would be able to get his teeth into it. But if King is right about the size, then it might still be small enough for an averaged sized adult beardie to choke on. Also, between their hardness and their ability to bounce back with almost as much force as they hit a hard surface with, superballs may also pose a risk of injury -- what if the beardie were to accidentally get hit in the head with the ball?
Probably not a good idea for several reasons. I would suggest observing what sorts of things your beardie seems interested in playing with, and try to come up with some safer options.