I would contact the hotel in advance or ask the Marriott elite reservations people the question and have them note the answer on the record of your reservation in case an issue arises. I did this at the aloft PDX (Starwood) when their park and fly rate was cheaper than anything else and I had a flight the next day, after spending several days in a downtown hotel. No car and no problem, but I did have a flight and used their airport shuttle.

I've never been asked for a boarding pass either.

One time I found a good rate that included breakfast for two downstairs, but was tied in to a sporting event or something like that. I called and asked for clarification if it mattered if I had tickets or not, and it did not.