ROR sitemaps are completely useless. None of the search engines support them. But they all support the sitemaps.org format. Needless to say you want to use the on they support and ignore the one they don't.
ROR sitemaps combine the detail of Google site maps and the simplicity of RSS sitemaps, then go even further. Using the ROR format, you can turn this 'site feed' into your product feed, an article list, a staff biography sheet, an event listing, and so much more.