I use forest bed and have never misted the tank. The substrate is very dry, so what I do do when he's in shed (he won't use a humid hide) is wet about a cup of it, then spread it around the open area in the tank. He doesn't lay on it, but it does increase the overall humidity thus aiding in a healthy shed.
Last week I rewet then baked it to help disinfect it, and it will stay damp in the tank for a few days at least. When it's wet, my snake LOVES to burrow and hide underneath it. Like JT said, my concern is a risk of a respiratory infection, so I like to keep the temps up a bit during this time to help dry it out faster.
It in indeed very damp and COLD under the surface (even over the UTH).