Question:

Can you limit the access that RMS has to Office 365 calendars so that RMS does not have access to all calendars/mailboxes in the tenant?

Answer:

You can use Application Policy to limit the access of these calendars. You will still see the calendars listed in the in the Scheduling Plug-in however if you try to map that resource you will see the Hotlist Notification as "Scheduling Resource Synchronization Failure". If you try to book meetings, then will get an error that the booking as failed. 

To go with Application Policy approach, below listed are the steps we need to follow:

1. Create a 'Mail-enabled Security Group' and add the 'Rooms' to it.
2. Create a new Application Policy for the Azure App that is going to be used with RMS-SCH-EWS and provide ‘Restricted Access’ to the Group created in Step #1.
3. Use the Azure App with RMS-SCH-EWS, which we applied the Application Policy, above.
4. In the 'Resource Profile' tab of RMS-SCH-EWS, enable only the rooms that are part of the 'Mail-enabled Security Group'.
5. If you enabled any Rooms that are NOT part of the 'Mail-enabled Security Group' and mapped it to a location of RMS, then will get the Hotlist Notification as "Scheduling Resource Synchronization Failure". If we try to book meetings, then will get the "Unable to make meeting reservation".