VAC is in GMOD, but isn't active anymore. Even though it states on the GMOD Steam page.
I've been using scripts in GMOD for years, no ban. It is very unlikely they would enable it again, and if they did, like 70% of the GMOD playerbase would get banned.
I think GMod is VAC secured but it doesn't actually do anything. You can still inject, most cheats/hacks are client-ran LUA scripts anyway so... no, VAC really has no affect on Garry's Mod servers.