I had a problem in that updates were not successful on the cluster. Many reports for the error message “Upgrading a VMware ESXi host fails with the error: Cannot run upgrade script on host” point to removing the FDM installation using the uninstall.sh
/opt/vmware/uninstallers/VMware-fdm-uninstall.sh
However I didn’t have the uninstallers directory on my ESX boxes. My solution was to enable HA on the cluster then removed HA on the cluster and after that updates worked fine.