It would appear that although there was once a reliable way to play Half Life 2 and it's episodes in VR, updates to Garry's Mod in the last year have now made this impossible and ruined all the mods built to make it work.

You can kinda get in there and stand around but the weapons don't work right, the SMG spits out missing texture errors instead of casings, and I couldn't figure out how to make any weapon do an Alt fire.