There are 3 skin VMTs that make up each TF2 Zombie. In this test, I added the VMT Command $MostlyOpaque to the Red Heavy and the Blue Scout Zombie VMTs. Where it doesn't completely fix the transparency problem, it culls it quite a bit. While the camera is moving, you can see the background move through the Blue Heavy and the Red Scout (The skins I didn't add the command to). The effect is significantly reduced in the Red Heavy and Blue Scout. (The skins I added the command to.) The light auras you see around the zombies are light kits I added to spine bones in the models. The video was to dark to show the problem so I added the lights to make it more visible.