Don't know about wild moss, but with java moss, you can rinse it out in a mild bleach solution. Perhaps you could try it and see if the wild moss lives.
Chances are that the critters in the wild moss will do no harm to you're adult frogs, but rather become a food source.
Frog eggs are another story!
for a while I was using wild spagnum in my substrate mix, without sterilizing...figuring the microfauna would be good food. As I found out that moss was the source of nematodes that were eating my imitator's eggs (I think). I always wondered why I never seen frogs in that swamp where I get my moss...I think I know why now!
The moss will be safe if you collected it from a safe place. I collected mine from alongside my deck and have had no problems with my frogs. It's actually growing a little bit in the dark corners. It looks good AND is free! Just be sure where you collect it from hasn't been exposed to fertilizers or chemicals and you're good to go.