I always used the famous and known Platinum Amex CDP with Hertz without any trouble.
However looking up rates with it now it states:
You may be required to provide proof that you qualify for the discount code (CDP) when you collect the vehicle. Please refer to the terms of the offer for further information.
It never said that before on the webste. Anyone any experience with it and knows if they now actually actively check if you have one or not?