Ups, I didn't think through you can't run this test on the same machine where you intend to host jsreport...
Anyway, the unoconv is just a wrapper for the LibreOffice API, its source can be found here
https://github.com/unoconv/unoconv/blob/master/unoconv
There could be a problem with some config, but I gues the problem is somewhere else...
If you run jsreport on the same machine as this test, I guess it will work as well right?
In this case, it would mean that LibreOffice is still using OS machine fonts even when you embed it.
Fonts can't be installed on the jsreport server cause it's problematic to deploy custom images to Azure.
What Azure service do you use? Perhaps you can deploy with Docker and build an image with the requested fonts.