ESX Version 5
You need to use the CLI to edtit this per below :
PowerCLI C:\Program Files (x86)\VMware\Infrastructure\vSphere PowerCLI> get-vmho
stsnmp | set-vmhostsnmp -enable:$true -readonlycommunity @(“%communityname%”) -addtarg
et -targetcommunity ‘%communityname%’ -targethost ip.ip.ip.ip
PowerCLI C:\Program Files (x86)\VMware\Infrastructure\vSphere PowerCLI> get-vmho
stsnmp | test-vmhostsnmp
ESX version > 5
esxcli system snmp set --communities %communityname%
esxcli system snmp --targets ip.ip.ip.ip@162/%communityname%
esxcli system snmp set --enable true
esxcli system snmp test
/etc/init.d/snmpd restart