Every distribution has its own conventions to package scripting languages addons (perl modules, ruby gems, etc) as native packages. This allows packages to depend on those addons honoring the package dependencies, and at the same time, look like the addon was installed the scripting language tool (cpan, gem).
I created a template for openSUSE-like rubygem-* packages, and David committed it upstream.
So, to create a package for a gem:
gem fetch foo
gem2rpm -t opensuse.spec.template ./foo-1.1.gem > rubygem-foo.spec
Build and tweak it. Make sure everything is alright. Some gems work out of the box, some not, but still gem2rpm saves 90% of the effort. Consider submitting it to the project if you are willing to keep it up to date ;-)