although your snake will certainly drink from a normal water bowl, I've seen a lot of herps that will drink from moving water more readily than standing water. It's a smart way of doing things from an instinctual standpoint (flowing water in the wild would normally be fresher and cleaner than stagnant water, and it would have less possibilities for bacteria and other nasty stuff to grow in it.
I think if you wanted to use the waterfall you could AS LONG AS you took extra precaution with the parts mentioned above. You might wanna watch your humidity levels though with something like that in the viv.