I experienced how the procedure works returning from the Gathering last year. When we arrived at CUS we were directed to the old Metropolitan lounge. Once there we were all provided with a pretty nice box lunch and soda from a local deli. While we were eating, customer service folks were going through checking names against what I presume was the manifest, once they were done they started to process folks. We had more folks than the sleepers would hold, so it appeared to me that they put the coach passengers in the sleepers and sleeper passengers got taxi and hotel vouchers. Those staying in the sleepers were escorted out to the platform with their sleeper attendant.
The process was fairly smooth with only the few of us receiving vouchers having to go to the customer relations desk. For once it appears Chicago got something right!