Is there a way to enable hotkeys while a fullscreen app is running (like a game)?

Not to my knowledge. At least not from within LS, maybe it could be done with some standalone hotkey app (but that would probably conflict with LS anyway).

May I ask why you want this behavior? The last thing I would want personally is having LS hotkeys active when I play games...

I want to be able to use my volume and mute bangs.

Do you have any extra "media" keys on your keyboard? If you map stuff to these, it should work. At least it works here, on a Logitech UltraX keyboard. Only tested with one game though (Unreal Tournament).

This will help you a lot... Read on
http://www.nbi-studio.com/news.php?extend.6