I'm not a fan of not telling the truth to the hotel, but it sounds like you made it clear that they would be staying in the room and the hotel did not object. I would make sure you have something in writing about using your Amex card, though. I usually get confirmation via email prior to doing that and give the person using my card written authorization to bring to the hotel. Most hotels have a form that you complete. I could see a situation where they aren't allowed to use your card and that could trigger an issue with the platinum override. Making sure the CC issue is taken care of in writing would decrease your chance of having that happen.