You could try to switch from the games from DX9 to DX11 or vice versa. DX9 is the preferred mode, since it has Geometry 3D, but if one of them does not work, the other may be worth a try.
This has to done with an .ini tweak unfortunately. Here you find a short tutorial for Dirt 3: http://forums.steampowered.com/forums/showthread.php?t=1907032
dirt2.exe and dirt3.exe should remain on the exclude list. These are the launcher programs, not the actual games. vorpX should not hook them.
You can do a full factory reset in the config app (trouble shooting page) to bring them back if you can’t add them back manually.