Sure that this has been done before.
Me and tother half and 9 month old son are staying in a small (15 bedroom) family run hotel for a weekend later in the month. They have a lovely restaurant. They are very child friendly, and they advertise themselves as offering baby monitors. They said on the phone that they could give us a room with a baby monitor so that we could have a meal in the restaurant at night. They said people did it all the time and it worked fine.
The wee boy goes to bed about 7 and always sleeps soundly till atleast midnight. We'd be downstairs (the room's on the first floor) a few hours tops with a monitor. I don't think I'd be comfortable doing this in a large hotel with loads of guests and staff, but this seems different.
What do you think?