Correct me if I'm wrong, but aren't those Google Forms? I don't think I'd trust my credit card information to one if it's reminding me not to enter my password in one!

This "hack" appears to just be abusing a conference organiser's pre-arranged rate for hotels near the area. I'm assuming the Google Form submits your information to the conference organiser, not to the hotel. They should (but apparently aren't) cross-reference the attendance list before passing the approved reservation to the hotel.