How do I get a list of Virtual Machines that have a Commvault client installed?

Hi Japplin, 

There are a couple of ways to check this. The Health Report in Webconsole or Command Center has a tile called 'Clean up'. The Clean up details has information about 'Clients with Duplicate Backup' – this will include 'Clients with Double Backups (VM's Backed up by Virtual Server Agent and other Agents)’

Health Report: https://documentation.commvault.com/11.21/essential/38637_health_report_overview.html

Clean up:

https://documentation.commvault.com/11.21/essential/92364_health_report_cleanup_tile.html

I hope this helped