Daniel - Yes, this is possible. You'll need to do these steps, in order.

From the CLI or FilerView, create the vlan (vlan create)

From the CLI, create a separate IPspace for the vlane (ipspace create)

From the CLI, assign the vlan interface to the ipspace (ipspace assign)

Finally, either create or modify an existing vfiler, to use the ipspace that you have just created. Assign the required IP address to the vfiler. It will use the VLAN you have specified inside the IPspace.

Roger Weeks