My original idea was that the mentors help each HoH, visiting them from the "golden door" in the HoH room so that others don't know about it.
But if all the players get mentors. they could just meet in the DR. But I sincerely hope that the mentors are kept hidden away.
BUT, they should still show us any mentor/player talk in the DR on the feeds. If they keep that only for the shows, the whole thing will suck because it will be heavily edited, and possible rehearsed.