Unfortunately, as they're a private institution and they're up-front about this requirement, then, yes, they can do as they damn well please. If this was something that they'd instituted after 10 or 15 years and then laid people off due to, that'd be grounds for suit.

Otherwise... I thought Concordia was a Catholic college? Asking for 'witnesses to Christ' puts them way over on the (*icky icky poo*) evangelical side. *scratches head* Although they are just across the street from the Lutheran Synod's local HQ...