I'm just circling back to update this with some info. I contacted Delta today and they confirmed that ticket agents open the desk at 4:00 a.m. even though their flight has a scheduled departure of 5:17 a.m. Seems tight, but I guess they routinely make it work.

I wonder if the 45 minute cutoff for luggage at DFW is fungible for these extremely early a.m. flights? I would hate to be flying coach with checked bags on that flight.