IMO, the bottom line is every situation is different. Example, this spring in GSO we showed up to find that a *possible* tornado had come over the field. NWA, Comair, AWAC planes all over the ramp grounded. Needless to say lots of cx'd flights. An offline pilot in jeans and sandals came up to ask if she could sit up front. There were 20 open seats last night and now 1/2 the flights were cx'd. On her way to a friend's wedding, given the cirumstances, I let her on. Would other people, maybe? Unless it specifically says something in the FOM, I treat every situation as it comes up.