I'm using XPLIT broadcaster to stream and I had this problem a few months ago as well..
Every game works fine except gunz.
I've tried running both programs as admin and still fails to show up.
The problem is that I can add the source to xplit but I get a black screen instead of gameplay.
FGunz will work in windows mode and shows up on stream but it doesn't work with fullscreen mode.
Any solutions on how to fix this?