I kinda like the idea of trapping a bunch of incorporeal creatures in a tightly sealed treasure room. Boy are they going to be pissed when they're finally let out by that unexpexting group of treasure hunters.
this could be a mean trap for scroodge's money vault.
I doubt I would go with the idea that a supplemental book supercedes a core rule book as not everyone uses all the books even if they are WOTC. If the MM says the same as the MMIII then that would be better source but if they disagree; I can't check at the moment no books handy, then whatever the MM has would be the primary one I would go with. Of course that depends on the SRD version as well, as that would be good source.