Why not have VLAN 1 untagged on the router (and other network devices)? That's a much more common configuration.
In any case, if the ICX won't let you remove untagged VLAN 1 from the uplink port, then just create a 'dummy' VLAN on the ICX that isn't ever used for anything, make it the untagged VLAN on that port, and make VLAN 1 tagged on that port.
In any case, if the ICX won't let you remove untagged VLAN 1 from the uplink port, then just create a 'dummy' VLAN on the ICX that isn't ever used for anything, make it the untagged VLAN on that port, and make VLAN 1 tagged on that port.