Steve
To help easy your pain with losing mgt access to the freenas server, how about you leave nic1 setup for your vlan 1 mgt ip in access mode. Then create a lag interface with only nic2 assigned to it and try and get vlan tagging working from this point. If you are able to get vlans working on the single nic lag, then you can delete the mgt ip from nic1 and add it to the lag interface setup.
Just a thought
To help easy your pain with losing mgt access to the freenas server, how about you leave nic1 setup for your vlan 1 mgt ip in access mode. Then create a lag interface with only nic2 assigned to it and try and get vlan tagging working from this point. If you are able to get vlans working on the single nic lag, then you can delete the mgt ip from nic1 and add it to the lag interface setup.
Just a thought