I am an independent consultant that gets on projects run by big consulting groups. I am NOT an employee of theirs and have no ID. I have been doing this for many years and have never been asked for ID. If I was and had to prove it to get the discount I could not. I am required to get that rate for the project budget. If I didn't get the rate the project manager would call an fix it. I am Platinum so maybe that helps.
BTW what is a GIBS?