Actually, at least at MSP Terminal 1, there are always airline employees in the CBP areas. They lock and unlock the doors from the jetways into the CBP area, direct and manage passenger flow through the correct lines for processing by the CBP agents, and help the passengers in the baggage claim area. However, they do not have anything to do with passengers exiting from CBP.

At MSP Terminal 1 all the international flights are SkyTeam, so the airline employees in CBP are all Delta staff. There are also MSP travelers assistance volunteers, of which I am one, helping in the CBP areas in very strictly defined ways, especially in managing the passenger flow through passport control. Those volunteers have received extra training and additional security badge clearance than other airport volunteers.