I've shot VB all season long using a flash with zero complaints. The athletes don't even know you're using a flash because they are focused on the game. After you shoot a few VB games it becomes apparent that VB is quite predictable and you can zero in on whose going to be getting the ball just by the way the game is set up to be played. Of course, shooting in low light without a flash requires a fast lens using a flash has worked well for me.
It is not a question of whether the volleyball players will be bothered by it, its a question of whether the officials and coaches will allow you to use it. Volleyball is very conservative and most venues are going to frown on flash. But I agree that it would be unlikely to have any effect on the players.
As for it being predictable, I think it may well depend on what level volleyball you are shooting. I find it pretty hard to predict the really good action, and even when I can predict it, getting the peak shot is still pretty difficult since they don't ever take possession of the ball.


