Yes, it ust be Full-Screen or Windowed Full-Screen, I believe.

ah ok, i did like plenty of testing without any game up lol

Ahhh XD

Yes, it automatically detects when a game is up in full-screen. Then it runs.

Update

Got the Ventrilo built-in overlay working.
It's atrocious X_X
It's not transparent so it takes up a large portion of the screen; no matter what I'm doing, it's in the way.

I did this by editing my registry as a website instructed to fix overlay capability for Win8.

I thought it may fix the VoiceOverlay program as well, but it did not.
I then tried adding a Registry Edit for the program itself, separately from the one I did for Vent, and that failed to produce results as well.
I know it's got to be possible now. I just don't know what exactly I need to do, edit, or insert.