Hi.
ESXi dosnt support SNMP GET, only Traps
by looking at your check string i assume you are running a Nagios/Naemon based monitoring.
There are tons of VMware ESXi plugins at Nagios Exchange that pulls hardware status directly from the ESXi native agents.
OMSA VIBs are not neccesary unless you are using OpenManage Essentials and not having iDRAC Enterprise on your servers.