When Trigeo was still selling the physical SIM appliances, they couldn't very well rely on VMWare or Hyper-V for HA systems. The LEM VM is the same code-base as the SIMs, and so there are some commands that no longer apply still in the CLI and documentation. However, I've spoken with the LEM devs on a few occasions, and none of them were very happy with how the SIMs handled HA, and the virtual infrastructure tends to produce a much better result. I suppose, theoretically, you could setup and license two LEM VMs and set them up as a "legacy" HA pair, but there's no reason to give Solarwinds extra money when VMWare or Hyper-V can accomplish HA with fewer resources.
Addendum: The reason it's probably still there is that somewhere out there is a Trigeo customer running SIM appliances that are 10 years old who will never virtualize and will run those boxes until the sun dies or they do. Those commands and references are there in case that guy ever wants to upgrade his HA setup, but for new customers using the virtual appliance, there are better ways to accomplish HA.