AFAIK no they didn't, Valves engines are from the Quake lineage and still use PVS but they only added serverside fog-of-war to Counter Strike relatively recently in ~2015. As the Valorant article goes into, it's a harder problem than it appears because you need to allow the client some wiggle room to know an enemy in coming around a corner before the player sees them so that lag compensation and shadows work correctly (Valorant sidesteps the shadow issue by simply not having players cast shadows). Plus PVS is quite coarse so if you want precise culling you need a more computationally expensive solution.

This video compares Valves own fog-of-war implementation to the implementation used by FACEIT, a third party competitive matchmaking service, which shows there's a pretty wide range of trade-offs to be made. Valve went for conservative and fast, while FACEIT went for aggressive and (presumably) slow:

https://www.youtube.com/watch?v=8w1ICIBO3D4

Valves implementation is better than nothing, it at least stops cheaters from knowing which direction the other team is going at the start of a round, but beyond that it doesn't stop them from knowing exactly where most enemies are standing around corners because the serverside visibility checks are so coarse.