It sounds like the utility that you're using is not shutting down the guests ... If your VM(s) have VMware Tools installed, however the utility 'hooks' into ESX should initiate a guestOS shutdown if it can and it may have an option to hard power off and then power down the host. I would probably contact the vendor providing this utility and see if they know what the issue is, I don't think it's not a VMware issue if the host is powering down but the VM(s) are not shutting down.
If this utility can be installed on a standard Linux system, you might want to take a look at this shutdown script that I wrote: ESX/ESXi APC/APCUPSD Host Shutdown VI Perl Toolkit Script (ghettoShutdown.pl/upsVIShutdown.pl) -- [ DEPRECATED ] The script was created against APCUPSD but you can substitute pretty much any UPS utility that can monitor your UPS and provide the appropriate calls to the shutdown script to power down the guestOS (soft / hard) and then power down the host.
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at: http://engineering.ucsb.edu/~duonglt/vmware/
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