I work for a company that is partially owned by a Fortune 100 company and we have their corporate rate code linked to our travel website, (although it is one of the ones that is very easy to figure out). In 4+ years I've never been asked for any ID, although a few times a year I get the question of "what company are you with?"

A coworker of mine claims he was asked once and given a hard time because we don't really have ID's and our business cards don't say anything about the company whose code it is. Supposedly he had to pull up a news article that said our companies were affiliated.

Edit: To the OP, basically the consensus seems to be they don't ask much. But if they do, I'm not sure a business card of someone who isn't you would be valid...