Hi @cyril.og!
You are indeed right. If you can accurately generate the compilation database, convert it and feed it to the analysis, you do not need to build the project inside the build-wrapper.
But, please do note that this is a workaround provided to help non working cases. It is not thoroughly tested and it is not officially supported.
If an official support comes up, the ticket will be updated accordingly.
Cheers,
Geoffray