The hmp-snmp package must be installed in order to use the SNMP functionality with the hardware management agent (svc:/system/sp/management:default). To check to see if the hmp-snmp package is installed, type the command:
pkg list | grep system/management/hmp-snmp
Packages with an "i" under the IFO column indicate that the package has been installed.
SNMP configuration needs to be done manually. See Configuring the Hardware Management Agent and Hardware SNMP Plugins.