Don't know about the hubs, but at some stations there is monkey business with the upgrade list. I commute regularly from PBI in Florida, and there has been some controversy about this, although it does not involve employee travel. When you bring it up with the company, they don't want to discuss it. While you generally don't get very far with gate personnel with threats, one tack I take from time to time is to ask before boarding "I assume there are no non-revs on here?". This lets them know you are wise to the potential, and probably not somebody to fool with. It sounds petty, but frankly, there is a lot of "screwing around" that occurs with this stuff. Upgrades are not free. If you qualify, it means you have spent sufficient money with the company to get there. Airlines consider the perk as a marketing cost the pax has bought with past patronage.