Deploy ESX virtual machine from template with esxcli

vCenter is a management tool installed on either a physical or virtual Windows 2003 or 2008 server. vCenter in turn manages ESX and ESXi hosts/clusters.

It sounds like you're trying to directly add an ESX or ESXi server when in fact its meant to communicate with a "vCenter" server.

The easiest way to do this would be through PowerCLI, which is a PowerShell plugin for vSphere. With that you can use the Set-VMResesourceConfiguration cmdlet to modify the resource configuration of your guest machines.