Hi Andy,
With regards to iSCSI, yes you should have one interface active and one as unused, in fact this is required for the VMKernel port bindings to work.
For NFS, you can have two or more NICs set as Active, and rely on the "Route based on physical NIC load" policy if you have distributed swicthes.
And of course, your correct that IP storage traffic (as well as vMotion / FT) should be on separate non routable networks.
Hope that helps.