To answer your question first: Beaked moss probably does not carry the snake specific mites that can harm your snake. If anything, it contains wood mites or something similair. If you spot any kind of mite in the enclosure, order some provent a mite and treat the enclosure accordingly.

To address your husbandry: The fact that you are using moss means that your husbandry is not spot on like you say it is. Sounds to me like you are struggling with humidity and that your little guy only feels safe in water. Get him in a smaller tank or tub with two identical tight fitting hides. An 80g tank is not for a ball python. Maybe you can find a different species of snake or reptile to go in there.