We have FAS2050 and have a single port 10GB card in each controller.
These cards will be dedicated for NFS and iSCSI, each one will connect to one of two stacked CISCO 2960s giving each switch 10Gb uplink, and then the servers will connect to one 1Gb port on each switch giving 2Gb storage path (iSCSI or NFS) to each server.
So, should i separate iSCSI and NFS traffic by using VLAN tagging on NetApp side and switches or is it ok to run both iSCSI and NFS on the same VLAN?
For me that comes down to how you're using NFS -- iSCSI is pretty much always for server access but NFS can sometimes be for "client" access (Linux/Unix desktops/workstations) and sometimes for "server" access (VMware mostly...also Linux/Unix servers).
If it's all "IP Storage", I'd just let it ride on one VLAN. Otherwise, I'd do 2 VLANs just so you can block iSCSI access from anything "client-ish" boxes.