Will have to clear things up a bit since we're talking about several modes by now and I also went to talk with our GM guys.
1. STORY: Shroud works if in Leveldata, "Set hide shroud" is False
2. GM: No shroud. At all. Not for GM, not for players.
3. Editor: Again. No shroud at all.
Ok, so it's impossible right now to have fog of war in GM mode. I hope you can add this feature to the game, it's one of the most important for a GM.