I wrote this little wordpress plugin to integrate Jerome's Keywords plugin with Google Sitemaps plugin so that the generated sitemap will also include tag pages. This plugin was inspired by a an addon that integrates Ultimate Tag Warrior with Google sitemaps.
You will need WordPress 2.0.x, Google sitemap 3.0beta and Jerome's keywords 1.9 for this plugin to work. It would be easy to make this work with Google sitemap 2.x so if you need it just let me know.I don't know how this would work on older versions of Jerome's Keywords cause I haven't tried that.
Download: Google Sitemaps - Jerome’s Keywords Plugin