Might it be possible to create a zone with only the one NIC assigned and run the CIFS from there? Or is CIFS like NFS and being a kernel function it can't be run from a non-global zone?

# on entering init state 3. # Issue the command 'svcadm enable network/nfs/server' to # run the NFS daemon processes and the share commands, after adding # the very first entry to this file ...