no, its not really necessary. humidity doesnt need to be that high and proper humidity can easily be achived by something as simple as switching to a UTH or moving the water bowl partially over the warm side.

plus, if the ball is small enough you might have to worry about it getting stuck in it. i read a story in reptiles magazine a year and half or so back about a baby ball that was stuck in a waterfall for two weeks. the owner tried cutting it out and accidentally cut the snake.