I have all my kids sleep in one open space (the daycare is in the basement and is all open) and I don't have any issues. I put them down and leave them for 2 hours. I can see them on my video monitor but I rarely go downstairs during nap. They all sleep great. Sometimes one kid will wake up early but they have learned to quietly stay in the PNP/cot because they will be the last one allowed to get up and play after nap time if they are disruptive.

The room is mostly dark however I leave the light on above the stove so my 3.5 yr olds can read when they wake up.