I got this as well and booked the holiday Inn at Melbourne airport through an online site. My flight had been delayed and I wanted to spend the night there, this was at 3:am. Upon entering the lobby it seemed the two people at the counter had no interest to make an eye contact or looking being approachable. I initiated the conversation after they both ignored me and the guy straight away said the lady will help me. There was no help and it seemed she didn't want be there nor to see me. She said check in was at 2PM and after I suggested that I needed the room because my flight was cancelled and if she could help, the guy walked over and said where have you booked it and I mentioned online through a third party, he said can't help you and there are no rooms. Initially it seemed they wanted to help but not sure why they didn't like mentioning third party.
I mentioned about my diamond status and they couldn't give a rat's tail about it. And said no room.
I walked out of there at around 3:30AM.
So this diamond status doesn't mean anything.