Hackers are plenty rare in TF2. I have only seen one, and for all I know, he was glitch abusing or using some script, but he could build multiple sentries. Like 6 of them pinning the other team in their base. Forgot the map and the gametype, but it was amusing to watch.
Other than that, VAC actually works in games besides MW2. Its depressing to see that most peoples opinions of VAC are formulated by MW2, which has shit defense against hackers thanks to matchmaking.