Exchange server 2016 is fully supported.
Regards to Oultook 2016 it is not supported for any on-premisis Exchange Mailbox Backup.
As Outlook 2016 has different mode of installations
Click-to-Run and MSI
in click to run mode of product case with different build versions Backup may not work.
So we are not cliaming support of Outlook 2016 version for Backups.
If your in environment Backup /restore of Exchange is working fine, then I would say you doesn't need to worry.