Welcome to the VMware Communities forums. The current release of ESXi only supports SNMP traps. The original intent was to move away from SNMP to WSMAN. A future release of ESXi may support SNMP get, but for today you'll need to do something else.
If you search for Nagios and ESXi you'll find a number of solutions, or you can monitor with a python script. See this as an example - http://communities.vmware.com/docs/DOC-7170.
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It works very well, also with PNP4Nagios.