Non-global zones use the default scheduling class for the system. If the system is updated with a new default scheduling class setting, non-global zones obtain the new setting when booted or rebooted.
The preferred way to use FSS in this case is to set FSS to be the system default scheduling class with the dispadmin command. All zones then benefit from getting a fair share of the system CPU resources. See Scheduling Class in a Zone for more information on scheduling class when zones are in use.