@KatherinWinter no he pulled in gem as well, he didn't leave him out, otherwise the 'monsters within a time allotted by our current benefactor, mr Gem' part of his speech would of been pointless. But if someone else was walking around or even entered the current room wouldn't be able to see them and those inside wouldn't be able to see those outside.
Basically they are entirely split off from those outside, the dungeon will copy it's surroundings if Charles doesn't select a dungeon type, and then pull in people Charles designates on creation. Which was Mr.Gem and all of the other Gems in the room along with himself of course.
The dungeon can be closed should Charles leave the dungeon causing everyone to be pushed out (I.e. his ID Escape skill), is killed, or a strong enough energy force hit the dungeon's barrier that can over power Charles' ability.
Also I'm making a monster sheet currently for all the monsters of the dungeons he can make currently (which would be Zombie and Ghost, then the Zombie and Ghost Bosses), figured if I do this could make things more simpler in the future if I keep adding to it as more dungeons he can make which his skill goes up.