Hi Thomas,
after some Troubleshooting with Symantec support we are able to backup and (!!!) restore auf Exchange 2013 DAG farm.
Our Exchangeteam use the new IPless DAG-Cluster.
There are some setting we have to set.
+ Configure DAG-Name as DNS-Alias for one of your DAG-Nodes
(https://support.symantec.com/en_US/article.TECH223843.html)
+ "Netbackup Client Service" and "NetBackup Legacy Network Service" shold run under a Serviceuser with Exchange-Rights.
+ Configure "Distributed Application Restore Mapping" for your DAG
+ Allow Connect back from DAG-Node to your Masterserver
+ Backup only active copies (Setting in your Policy) in Policy type "MS-Exchange Server" and use the DAG-Name as Client.
I hope this short description helps to find your Problem. Otherwise you can contact me for further details.