Not used shadow troopers yet, but if they are set with a NPC_targetname, they should not spawn until triggered. There is probably a way to make them invis when spawned, like in SP game, but again... I have not messed with them yet.
I tried GTK 1.5 and found it to be full of bugs and many components did not work correctly. I went back to 1.4.0 and have had no trouble setting trigger brushes. Are you working SP or MP? The entities available depend on this.