I've been trying to get our core game mechanic (or a rough version) working in UDK so we can start whiteboxing and testing our gameplay as soon as possible.
This is what I've got so far.
Picking up the shock rifle, makes the currently invisible blue sphere visible and spawns an enemy bot at a set location. This can be triggered multiple times, as other bots/ players pick up the weapon the mesh will become visible to them and another bot is spawned. This is when things start to get a bit mad.
Picking up the rocket launcher does the same for the red mesh.
Eventually I hope to have enemies in the level already and have them become visible when the player picks up a certain item. From what I can tell this will most likely be some sort of material effect using matinee but I'm still working on this!
Here's a shot of our Kismet setup.