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.