Hello,
I’m a lead developer of the team who is responsible for DxO PhotoLab for Windows so probably I can help you on this topic and answer your questions, if any. Feel free to ask me 
As I know we added the CLI many years ago for the feature that was abandoned somewhere in the middle of its development. However, what you mentioned above looks promising for us so we can decide to resurrect the CLI, update it, and make sure it’s production ready (tested and documented).
For the moment I can share our internal documentation for the CLI interface but you should keep in mind that it’s unofficial, i.e. there is no any public obligation on us regarding it.
@shaman Please confirm that you use DxO PhotoLab for Windows, let us know its version, and share your sidecar file that caused the error so we can investigate it.
Alex