Do I have to create an Oracle account on NetApp Filer and put the entry in /vol/vol0/etc/passwd?
You mean *by* putting an entry into the filer's /etc/passwd file, right?
It's always a good idea to keep a filer's notion of /etc/passwd file entries in sync with the rest of your network, but strictly speaking it's not often necessary for basic NFS operation. In fact I am told that in the early years of NetApp, before my time, filers didn't have /etc/passwd files at all. The NFS protocol just deals in UIDs and GIDs, and back then the filer had little need to know what user names and group names were associated with those numbers.
These days, there are features in the filer can benefit from knowing about username/UID correlations. The quota subsystem is one that springs immediately to mind. If you have used usernames in your /etc/quotas file for example, the filer needs to know what UIDs it should be looking for in the file system in order to charge space to the specified users quota. The Windows file service networking is another subsystem that can, in certain configurations, make extensive use of /etc/passwd (oddly enough! :-)), although it is also worth pointing out that day-to-day administration of a passwd file is entirely unnecessary when a filer is deployed in a Windows-only environment.
So, in summary, in a UNIX environment, I would make a habit of keeping the filer's /etc/passwd file in sync with the rest of the network as a matter of good practice, even though it may not be absolutely necessary. Don't forget that there is NIS client support in a filer to help you out in this area.
Keith