To add a mail enabled universal security group to a room mailbox calendar, so that they can review calendar, please follow these steps
1. Create the room mailbox. Note that room mailbox user account is disabled by default
2. Assign full access to the room using the security group
3. Have the manager(who is a member of the security group) login into his/her mailbox and open the room mailbox as well. (see other blog post on how to open another mailbox within your profile)
4 Open the calendar(belonging to room mailbox) and assign reviewer permission to the group
You are done. Now every member of that group can go to file, open other users folder, choose calendar and they can search for the room
Ex-Shell 