Yes, Hertz will look to validate coverage and if you are eligible. Additionally, if you are found ineligible, your rental could be viewed as violating the terms and conditions of the contract, making the contract null. This would mean that coverages by your personal insurance could be more problematic along with secondary (or primary as applicable) coverage through a credit card. You could ultimately be left holding the bag on the entire damage claim.

I never understood why people use codes they clearly know the are not eligible for, it's a form of stealing and ethics are highly questionable.