[Greg Titus]

So here is the source to an AppleScript droplet that will parse these sitemap files, make a shape for each web page with the file name as its title and with the full URL as an action, and lay them out hierarchically left-to-right.

Just paste this into Script Editor, save it as an application, and then drop any number of sitemap XML files on it to make a new OmniGraffle document out of each.