If you disable the watcher via the vorpX tray icon right click menu after launching the desktop viewer, vorpX won’t hook into any program anymore and you can play them using the desktop viewer. Strictly 2D only though, for any form of 3D vorpX has to hook into games directly.
Alternatively you can add the game’s main .exe to the exclude list in the config app. Saves the need for disabling the watcher.
Caveat 1: most games have to be run windowed or ‘fullscreen windowed’ to play them with the desktop viewer. Actual real fullscreen mode doesn’t get captured.
Caveat 2: don’t disable the watcher before launching the desktop viewer. Due to a little design flaw it requires the watcher to be active at launch. Never got the chance to change that until now.