Adding to this. The fact that the MGM + Marriott terms break out each program's reservation system and rates would indicate Marriott was not going to match MGM rates. Marriott understands casinos have other incentives for comping or heavily reducing their room rates.

I do wonder if there will be loopholes. Example: Booking originally MGM rate, then booking a Marriott rate, asking the front desk to extend your stay in the same room merging the MGM reservation into Marriott and earning EQN from the MGM night. From what I understand the hotels will have their own reservation system and Marriott would get the folio from them.

Same could be said from booking a Marriott stay, asking front desk to extend your nights directly, and whether or not Marriott would honor those extra nights.