Zenoss represents these VMware entities as devices:
Hosts (ESX servers)
Each of these categories is represented as a device class under the newly created organizer. For example, if the ID of an infrastructure is esxwin, then four device classes appear below /Devices/VMware/esxwin: Clusters, Datastores, Hosts, and ResourcePools.
Figure 48.7. VMware Device Classes
If the SDK endpoint is an individual ESX server, then the Clusters organizer will be empty. (A VMware cluster is a concept external to an individual host.)