Thank you for the reply. A colleague of mine went ahead and proceeded yesterday without powering down any VMs. The memory utilization on the hosts were 88%, and 95%. All of the VMs did successfully vMotion without issues.
My concern is I had a similar situation where memory utilization was high, and as I was putting a host into MM, two hosts briefly disconnected from VC. I cancelled MM, and the hosts did come back. I'm not sure what would have happened if I had let it continue, but memory % was in the red. I've never seen this happen before.