i need to restart my exch2013 MB servers that are setup as a DAG. need to install 3d party software, not exchange patch or anything.

If i just power off the VM (windows) technically my users should move to the cluster. or should I put it into maintenance mode first?

thank you

Please move all Databases activated on the server which you want to reboot to other mailbox server and then do activity.

To move the Databases

Get-MailboxDatabase -Server MBX1 | Move-ActiveMailboxDatabase -ActivateOnServer MBX3

here MBX1 - server which you want to reboot

MBX3 - Server where you are moving your active databases

I would still follow the same method to put Exchange 2013 into maintenance mode...

Below article will describe more in detail....

Exchange 2013 Maintenance Mode - http://letsexchange.blogspot.com/2013/03/exchange-2013-maintenance-mode.html