In my Hogfather RC2 wiki, the sitemap is working normally, so make sure that when you do the bug report you tell us as much about your setup as you can (PHP version, OS, etc).
You may also want to make a separate test installation on your server and try the sitemap with that. If the test wiki works and your main wiki doesn't, it could be something with the files.
EDIT: I misread, I was thinking of the user sitemap, it appears my XML sitemap will not load either.