Unfortunately Google won’t crawl Vaadin applications for the same reasons as with Extjs or any other library that renders the user interface using AJAX and Javascript. With Vaadin, only the Javascript required to initialize the rendering is included in the HTML page, everything else is fetched from the server using AJAX and rendered using GWT and Javascript.
I you want your Vaadin application to be crawlable by Google, you would still have to generate separate HTML content for that purpose. I guess this initiative could also be usefull:
http://code.google.com/web/ajaxcrawling/