And a "side-effect" benefit of your situation is that you could theoretically put the yellow DME tags on ALL of your checked luggage, skip baggage claim when you arrive, and just go down to the car rental desk.
DME only requires one person on a reservation to board the bus (having their ticket scanned as they do) in order for *all* luggage from that reservation to be cleared for transport to the hotel. That requirement would be fulfilled by your late-arriving friend. It might delay your luggage a bit before arriving at your hotel, but it'll get there.
You'll want to call DME and book it for the entire party so that you'll all get luggage tags and Disney will know what airline your bags are on. But you aren't required to actually *use* DME if you book it for everyone, just the one person who has to actually board the bus to clear the luggage.
Also, your friend should tell the CM at the DME podium how many total checked bags your group of 5 have.
-Rob
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