Purchased modules secret doors

Hello all  i will soon be DMing a campaign running the recent Dungeon of the Mad Mage module, and have it in print but not on roll20 yet. What I’m wondering is how do the purchased modules work secret doors because there are quite a lot of them. If the DM uses fog of war over the sections the players haven’t gone to but still lets them see the walls, will this also display the small symbols marking secret doors? How does that work? Any advice is appreciated. 

The secret door symbols are on the GM layer, the players wouldn't be able to see them.

The dynamic Lighting for the secret doors is a different color as well, denoting them as doors. They also hug the walls pretty well keeping the light and the vision (and the movement if you have Restrict Movement on) locked and in place.