My question is how to monitor with Nagios, the performance and availiability (machine stopped) of several virtual hosts running in a ESX. All plugins I've found are for 3.x API, running commands or with SNMP, but none of these methods are valid with the Vmware ESX 5.0
The CIM health checking python scripts all still work but the user must be an Administrator in ESXi.
Otherwise you can always monitor the virtual servers/services themselves.