I just ran through some what if scenarios in my vsim.. If fcp or iscsi or cifs are licensed (any of the 3) then cifs setup works. If one of the 3 are not licensed then you get the error that it needs a license. What I did find is that if cifs is already setup, it will still start and run for authentication even without any of the 3 licensed.
I would talk to your NetApp team and ask about a demo key so you can setup cifs, cifs setup, then delete the license. You won't be using it for protocol access just authentication and that would be a workaround (if approved). If you ever need to modify it then you would need a key again... you don't have iscsi or fcp licensed on this system and nfs only?
Something learned new again today...or relearned With the nfs only system a while ago... iscsi was free on all controllers back then and cifs setup would have worked the based on that. That has to be what happened when I setup cifs only for domainuser login.