Just a guess, but I think it depends upon the player.
For a kid who grows up wanting to play for Pitt, empty seats likely aren't noticed. He's seen it all before.
For a kid who's best offer is Pitt and his other offers are MAC level schools, the empty seats won't mean much. The chance to play at a higher level will win him over.
But for the kid with offers from Pitt and schools like OSU, Michigan, ND, PSU, Tennessee, those empty seats and the difference in game atmosphere from those other stadium has to be noticed. And there is no way it gives any positive edge to Pitt.