Yes you can use the moss for the Venus Flytrap. You're right, it would look very nice. Remember, no fertilizer or compost for this plant.

Orchids really don't need any sort of a medium. They are epiphytes, meaning, they take their moisture & nourishment directly from the air. The medium is used just to anchor it. Moss would be OK if not too compacted or you can use chunky bark & rock and just put the moss up on top for aesthetics.

In my experience, sphagnum type mosses can hold too much water if the majority of the mix for orchids, unless you are wiring the plant onto a tree branch. Other types of moss are most useful as decoration. On the other hand, sphagnum mosses work very well for Venus Fly Traps, since they grow naturally in peat bogs.