This is the same conclusion I came to. My alternatives are to do physical separation with no VLANs or VLANs on VIFs.
Physical separation would look like this
e0a - CIFS
e0b - NFS
e0c - iSCSI-1
e0d - iSCSI-2
Or, VLANS on VIFS as you suggest like this.
vif-front = e0a+e0c - CIFs
vif-back = e0b+e0d - vlan-NFS at nnn.fff.sss.xxx, vlan-iSCSI-1 at iii.scs.ii1.001, vlan-iSCSI-2 iii.scs.ii2.001
For VLANs on VIFS, LACP would be configured on the NetApp and on the Ethernet Switches with IP Load balancing.