Well, not really. There was a time when it was Valve staff and volunteer moderators under their direction. But that was before their discussion forums got integrated into Steam directly and there was a bajillion games on it.
Though I am confident they could actually hire people to handle it if they wanted to. Or were forced to. Steam makes a bit of profit, I'm sure.
"We invented democracy, existentialism, and the ménage à trois."
"Oh man... Those are three pretty good things."