SUBMIT YOUR GOOGLE SITES SITEMAP TO GOOGLE WEBMASTER TOOLS

The Google team hast announced that your Google Sites web site -- that is, the sites.google.com properties -- can be submitted to Google Webmaster Central.

Google has written up a help document on how to submit your site but also how to verify it.
Forum discussion continues at Google Groups.

How do I verify my site using Google Webmaster tools:
You can verify your site via the meta tag verification in Google Webmaster tools. Follow these instructions and paste the meta tag into the field labeled "Google Webmaster Tools verification" under More Actions -> Manage Site -> General. Please note: your site must be marked as a public site in order for it to be verified.

How do I submit a sitemap to Google Webmaster tools:
Once you have verified your site with Google Webmaster tools, Google Sites will auto-generate a sitemap xml file. Your sitemap will be generated at:

http://sites.google.com/a/(your domain)/(site name)/system/feeds/sitemap for Google Apps.
http://sites.google.com/site/(site name)/system/feeds/sitemap for sites under sites.google.com/site