If you think your hosts are old GSX or VMware Server hosted on Windows you can use PowerShell to see what programs are installed on each server.
If you think the hosts are esx or esxi then they should have web services running (I forget the actually name but its the web page on a host were you can download the vsphere client. Simply open a browser and type in http://your-ip-address If it is esx or esxi the web page will come up.
You can probably find a vb script where you can pipe in the ip address and attempt to open a web page.