You and I are on the same page my friend!. The exact situation is happening with me!. Difference is that I'm a network Engineer who is assigned a major project to upgrade a Flexpod solution in all aspects!, blades, vsphere and netapp!.
I've managed to upgrade all of them successfully. In the vsphere department; I've upgraded it from 5.5 to 6.7u3.
It's not an easy job, taking in mind that the solution is in production for years and contains tremendous amount of servers and VDIs.
Good luck.
PS:
I can advise you about the followings:
# before starting the upgrade, make sure your Servers HW can be supported by vsphere of the specific version. Use vmware interoperability matrice page.
# You cannot upgrade from 5.5. To 7 directly, you have to step it up in phases. 5.5 > 6.0 or 6.5 > 6.7 or 7. Your hardware will constrain you.
# Also, check cmware doc for upgrade guide lines.
About your question, you can add a vmk to the existing sw to connect to the new NFS storage. Depends upon your Topology and requirements.