One concern of mine in setting up a site on Google Sites is setting up a sitemap or an RSS feed. While I've only seen information on RSS Feeds for site "announcements", there is a sitemap already in place even though the information isn't on display in a Google Site management page.

To add a Sitemap to Google Webmasters, go through the normal steps for adding a domain. Select the option for metatag for verification. There is a place in the general settings to paste the code.

After your Google Site is verified add "/system/feeds/sitemap" to the field for the sitemap URL. Now you have your sitemap added for your Google Site. 

You'll probably have to wait a few days for the system to tell you how many URLs from your sitemap are in the index, but at least Google Webmaster will be aware of your pages for more complete crawling.