If you need to get an interface configured for a non-global zone and remain across a system boot:
In the global zone add an empty /etc/hostname.bgex file, where bgex is the interface for the non-global zone. This will plumb the interface when the global zone boots, but not configure it. Then use the standard zonecfg commands to configure the interface when the local zone boots. See Dracko #195 for some help on that.