Basically, my mom's spouse is a sound sleeper and fails to wake up to help my mom when she needs to go to the bathroom or if she wanders inside the bedroom. How would it work if a professional home aide were working overnight — particularly if my mom and her partner are in their bedroom with the door closed? I'm perplexed by the logistics of this.
Personally, I would start by putting a baby monitor next to mom, have the aid in a different room and respond to the monitor as needed. Then they can adjust the arrangement until they find what works best. I wouldn't close the bedroom door all the way.
Dementia is ever changing, so having a caregiver that understands that will help keep things flexible enough to keep working as the disease progresses.
If the caregiver hears mom, either through the door or via monitor (probably a better idea) the caregiver enters the room and takes mom to the bathroom and then walks mom back to the bedroom and helps her back into bed. If mom just needs a glass of water the caregiver can bring it. If spouse is a deep sleeper none of this would probably wake him.
There may be a time when getting mom up to walk to the bathroom is a bit more difficult and either a Sit to Stand would be needed or a bedside commode would be safer, or even changing her while she is in bed is a possibility. At that point a separate bed might be easier or a separate room. If they are not at that point now it might be a discussion that should be brought up for the near future.