hi,
first, NHA (NetApp Host Agent) is not needed for OSSV to work. Just install / configure OSSV, and start the snapvault backups OR if you are using Protection Manager (Ops Mgr. product suite), then, it can co-ordinate backups for backup schedule, retention, recovery....
Now, specific to your query reagarding why NHA is causing grief as it is, you may want to open a case with GSC to see what the problem is as I haven;t seen this behaviour OR shoot us some further logs, like events, etc..
Balbeer