The description page on Valve's website says that VAC is only active on multiplayer/coop/server related things. As the game features an coop mode you can be sure that it was meant to be for this mode.
However, we haven't added the VAC system nor we have develop the game. So we can't give you a proper answer on this as we simply don't know and all we can say is: use it on your own risk and ask the developers for a 100% correct answer.
//edit: For more information about VAC visit this link Link