calibre2opds is just a third-party tool to
archive an HTML+opds catalog which can be stored on a file server, that way you do not need to have calibre-server.exe running.
For instance, keeping a calibre2opds catalog in Dropbox, which doesn't allow you to install and run custom software in their cloud.
For your purposes it is irrelevant. Dunno why Marvin is having issues with the Content Server though.