Sorta. In branded zones it does allow for the use of /etc/system and it reads that file to set process control settings. For unbranded zones, you must use /etc/project or prctl to modify settings within a zone (including zonecfg settings).
I'm not sure why Ur looking for /etc/system in zones..
now in soalris 10u10 /soalrs 11..you can configure the kernel parameters as application/user specific
you can use projadd command to add the resources like shared memory
if you want add the parameters as global you can use
you can refer this doc what parameters u can add to zone with zonecfg
zone.cpu-shares (preferred: cpu-shares)
zone.max-lwps (preferred: max-lwps)
zone.max-msg-ids (preferred: max-msg-ids)
zone.max-sem-ids (preferred: max-sem-ids)
zone.max-shm-ids (preferred: max-shm-ids)
zone.max-shm-memory (preferred: max-shm-memory)