With regards to application documentation, library-web (the code
running both help.gnome.org and developer.gnome.org) has support for
modules driven by gnome-doc-utils or yelp-tools, that roughly means
Docbook and Mallard.
Modules that are parts of the modulesets published by the release team
are picked up automatically but it's also possible to manually add new
modules (adding a line to data/extra-tarballs).
You point to Gnumeric documentation. The good news is it is written in
Docbook, but the bad news is it does it with its own build system. It
will therefore need hacks in a few places, from a quick glance it
would need something in src/lgo.py (in extract_modules) to consider
the tarball relevant and containing a docbook documentation, and to
src/modtypes/gnomedocbook.py to hardcode the main documentation file
(gnumeric.xml, currently hardcoded in gnumeric-doc.make).
If there are other modules, I'll be happy to look at them and provide
guidance. Do you have a timeline for those changes? (The hackfest will
be last week of January).