ESP's work by you providing position information to them - if GM\GS\Admins are hidden, then you would have to figure out a way to get their position despite the status that is applied to them.
I don't know of any "hidden" status in the source engine, but if there is one, then it could also be in the code to remove their position from the local players information as well.
I realize not many of you guys do this daily, but alot of this stuff is common sense.