Assuming that you will have a dedicated VLAN (and subnet) for management and NFS traffic, it will always a good idea have a dedicated VMkernel port for the NFS traffic, even if management and NFS share the same physical uplinks.
The following blog post explain some reasons why to have a dedicated VMkernel port: The Necessity for NFS VMkernel Ports Explained - Wahl Network
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Richardson Porto
Senior Infrastructure Specialist
LinkedIn: http://linkedin.com/in/richardsonporto