From an M life manager in Las Vegas as per our discussion
Members must make a choice when staying at Hyatt properties between which program to earn in
At MGM participating properties in Las Vegas they may earn in both programs
This is in keeping with the published/shared communication from Hyatt (Hat tip to SFOcrew)
Members must be enrolled in both programs

Misinformation at all call centers
Do I hear coaching/training opportunities?
Hyatt Agents have routinely and repeatedly stated its always one or the other program one can earn in....... in all properties.
WRONG be nice but don't listen to them

M Life Agents have repeatedly stated including till up to late last night all properties both Hyatt and MGM properties member enrolled in both programs may earn in both programs
Wrong be nice but don't listen to them

Hopefully both programs will send internal memos and get up to speed!
This has been time consuming for all parties!