Yes, you can use your exchange mailboxes. So it would be best if you had the Room Manager for Exchange Version. All your exchange resources are managed in Exchange Online.
Exchange is the master. This means that your Exchange Admin manages all your policies and rules for Meeting room booking.
Room Manager adds the Meeting Room bookings with the details to the Room Manager Event Calendar list.
The Updates, changes, and cancellations of events done with Exchange meeting rooms are managed through Outlook for Desktop or Outlook on the Web using the Rm Outlook Add-In.
Please note that you can not book meeting rooms from the Room Manager site. All exchange room bookings MUST be made through Outlook using the RM Outlook Add-In.