Backup Windows 2012 with Backup Exec 2014

The recommendation to run the same OS (Win 2012 or Win 2012 R2) comes into the picture if using the VMware/Hyper-V environment and/or during GRT:-

Verbatim from Admin Guide:-

Symantec recommends that the Backup Exec server should run a version of Windows that is equal to or greater than the highest version of Windows that the virtual machines in your environment run. For example, if your virtual machines run Microsoft Windows Server 2012, the Backup Exec server should also run Microsoft Windows Server 2012.

GRT is not supported for the following scenarios:
- You must use a Backup Exec server that is running Windows Server 2012 R2 to back up an Active Directory server that is running Windows Server 2012 R2

Otherwise, your media server running Windows 2008 R2 is perfectly fine.