As stated in the KNX association’s “ETS5: Software requirements“, is not supported: “Installing and running ETS5 on a supported operating system in a virtual environment (such as Virtual PC, VM Ware, etc.) and/or via Remote Desktop is not foreseen. Working in such environments is at your own risk.”

As a longtime Macintosh user, I have been running the ETS (version 4 or 5) on different Virtual machine environments over the last 12 years. I started with VMware Fusion on a Mac, moved over to QNAP and ended up on preferring the Proxmox Virtualisation Environment for its ease of backuping and snapshotting. All of these environments worked if you managed to control the following two variables:

• Passing through the ETS USB licence key to the Windows host system.
  This seems straight forward, but I often fought with Windows not recognising the license key. Restarting the Windows system (sometimes even several times) mostly helped. The same was true for the USB-KNX gateway.
• The correct network interface settings
  Connecting the ETS to a KNX IP router / gateway requires setting your virtual machine to bridged network mode (your windows host must receive an IP from your main router). If you omit this, a double-nat might block you from connecting your ETS to your KNX bus. This was the case for me at least.