Tim,
It has been our experience that even if there are multiple network connections on the server, when it makes an NFS connection to the NetApp, it will only use one of those connections. We are not using NFS4/PNFS. Is Oracle NFS basically PNFS?
We had a process (non-Oracle) on a system a few years ago. We tried giving it an nfs mounted file system. The transactions drove the filers in the dirt. We switched the to FC luns and set up a "local" file system on the server. It is much easier on the filers and faster than the nfs file system. We're concerned that using NFS of any type may cause this issue again.
Unfortunately we probably won't find out if it is too abusive until they run full steam. At that point stopping them and changing the process probably won't be very popular :-)