An update to this thread: Last month, I stayed at the Crystal Gateway Marriott on a 2-night stay using the M11 rate. I was able to use the EEO certificate without a problem.

I'm currently at the Gateway on the 1st of a 2 night stay at a rate of $159 per night. The first night is business-related, but the 2nd night is on me. However, I submitted another EEO certificate at check-in to one of the front desk employees. At first, she didn't think it would be accepted, but after conferring with another person, she told that it wouldn't be a problem.

Please note that the person that refused the EEO last December was one of four people on duty this afternoon. It's amazing how talking to a different employee will give you different results. Fortunately, they didn't confer with him about the EEO.