the items created therein will have to be added to enemy inventories in order to appear. I haven't checked but I *think* if you mark items as clothing they can appear through lootboxes
the rooms created therein, provided you save them, should be randomly appearing alongside all the normal rooms on the relevant floor. one caveat is that because of how the floors are arranged, 'dead end' and 'straight' rooms are pretty rare
as you can tell parts of the editor are secret because they're a bit janky