This is a script I have hacked together to report on the DFS replication backlog numbers.  

A couple of things to note:

1. The opmanager service needs to be running as an administrator and not local service account or you will get access denied.
2. The script is configured to only show values greater than zero.
3. Command to run the script is cscript ${FileName}.vbs ${DeviceName}
4. As DFS replication normally always has some backlog I would not set the alerting values too low

Thanks

Greg