Configuring SNMP for ESXi is completely different from ESX.This will need to be run from a vMA or from the vmware-cli installed on your machine.
The command to run is:
vicfg-snmp.pl –server ESXiServer -c Community1,Community2 -p 161 -t trap1ipaddress@161/trapcommunityname,trap2ipaddress@161/trapcommunityname,trap3ipaddress@161/trapcommunityname
You will then be prompted for your admin user and pass on the remote system.