If you only have one IP on your NFS target then traffic will only be able to flow through one physical uplink at any given point in time, so two teamed NICs are sufficient.
OK - so I will have two physical NICS dedicated to NFS - can I use active/active on those NICs or active/passive? What should my load balancing policy be?
So it's a vmkernel port group and you're doing VADP-based backups right? Ok, I was confused because in your original post you called it a "VM port group":
I'm using VADP based backups. But with Avamar, it requires a proxy server on each compute cluster. The proxy server has a regular virtual machine IP address. The IP addresses for these proxy servers are all on one separate subnet from all other virtual machines. So yes it is in fact a port group rather than a VMkernel Port. The proxy server connects to the avamar management server. The avamar management server is connected to vcenter. By putting these proxy servers on a dedicated port group, is that in fact accomplishing the goal of isolating backup traffic or do I need to rethink that as well?