I have set the color's SOMETHING to different desktop and game levels in the ATI drivers... but I haven't seen the word "digital vibrance" mentioned there...
In nvidia I have only seen one place digital vibrace is mentioned, and that is as one of the 5 fields in "adjust desktop color settings"... no mention of game color settings though.
There is a "adjust video color settings" tab in the TV output zone, however the 5 fields there have different names (but the same icons as the desktop setting)... And they mention playing a video while adjusting this... So I don't know if "video GAMES" count as well... you could try to adjust the video and the desktop ones differently and see if you can detect a difference... maybe that would help
You could email nvidia about this, maybe there is something you can put in an ini file somewhere that will do the trick.