This goes for both new maps created from scratch as well as for existing maps being reworked for SE.
A dungeon that the player accesses from the travel map (the world) is at the location shown in the world. This means that if the player enters a dungeon in the middle of the desert (e.g. the Necros hub), the outdoor areas of the dungeon need to look it - there should be sand and very little if any vegetation around. This goes for all further outdoor areas of the map as well, not just right at the entrance.
As long as the player crosses to the next map of a dungeon hub through a door, tunnel or similar, i.e. the next dungeon map is obviously in the same world location, the same restrictions apply to all outdoor areas.
If the player crosses a magic portal to enter another dungeon map, the outdoor restrictions are lifted, since the magic portal could lead to a place nearby, a place at the other end of the continent or even to a place in another dimension.
There is one notable exception. If a dungeon map of a hub that the player reached through a magic portal has a normal entrance/exit connection to a world location, then this map's outdoor areas need to conform to that location.
The first map of a hub is accessed from the desert on the world map. That means the outdoors areas of the first dungeon map need to be covered with yellow sand.
The second map of the hub is reached through a simple wooden door from the first map. That means the player is still in the same desert area, thus the outdoors areas are covered with yellow sand.
The third map of the hub is reached by a magic portal from the second map, so there are no restrictions.
The fourth map of the hub is reached through another magic portal from the first map, however it also exits into the forest far to the west. The outdoor areas of the fourth map have to look like the player is in the middle of a dense forest.