This is how vent camping is defined in the motd:
-Vent Camping: Staying in a vent or hidden area deemed heap by admins with no intent of coming out. A player cannot repeatedly walk back and forth in the vent to avoid a slay. They are still camping the vent.
It says "a player", not "only CT's cannot". It's plainly put forward in the motd that no one is allowed to vent camp, no if's, and's or but's. If we allowed for T's to vent camp, they could just stay in a hard to reach/unknown vent for the entire round (ex: camping in the vent with the force field on Blackout), or wait for a CT to come around the corner or enter an area through a vent and knife him in the back once he comes through.(ex: camping the in the corner in disco on Carceris, waiting for CT's to tele in). All in all, no one can camp a vent, it's explicitly says that in the motd, and anyone that says otherwise is wrong.