Sam,
FYI I tried that and it did not work. I wanted to put the loopback interface into family ethernet-switching, but that apparently is disallowed. So I settled for putting it in the same zone as my vlan.0 (as you suggested). I also added that loopback interface into the same vr-instance as vlan.0 This unfortunately was not enough to get the SRX100 to bring up the vlan.0 interface eventhough none of the physical interfaces tied to vlan.0 were up.
Chris