Have you activated Analysis ID 905: Management Extender Status?
Check the log files on the relay - default path is
C:\Program Files (x86)\BigFix Enterprise\Management Extender\Plugins\VMware ESXi 1\Logs
ESXi systems are proxied by the Management Extender will have a Device Type of ESXi Hypervisor or ESXi Hypervisor Virtual Machine
Be sure to read through the documentation here: Patch for VMware ESXi