I know this is a bit late but still valid to answer. OpenMediaVault is Debian.
Put VMware Tools
If you use VMware vSphere Hypervisor (ESXi) go to VM > Guest > Install/Upgrade VMware Tools
We must log in with root user. It is better if we start with update all the software in system first then reboot one time.
Install compiler and Linux Header with command
Mount VMware Tools disc and extract file
Start installing VMware Tools with command
Then press Enter to all the questions to use all default answer. Then reboot again and it will be done.