I have added moss to my semi-hydro pots and have had good results. The orchids do seem to like it a lot and it keeps the leca from floating and shifting. Now repotting one of these pots takes a little more work as the moss doesn't just stay on the top buts grows into the pot.
I have live moss growing in my small yard in various places so when the dog dug up a little chunk to carry around, I brought it inside to grow. I thought about buying some different types from an Amazon seller and growing it in a bowl. It is pretty cool stuff.