I am not sure what exactly the question is, but hopefully the provided information will be relevant for you:
And last, going back to the "search-engine" problem - making search engines play well with partial page updates is a big topic in itself. There are vairous techniques and articles online that discuss how to tackle the problem. Most approaches to increasing the SEO rating of a page are related to a smart use of META tags, as well as how the URL is constructed (human-readable vs. pageid=12345678, for example).
In all cases, using RadXmlHttpPanel is to help you with specific scenarios - which makes it an unlikely candidate for building your SEO strategy on such a panel.
the Telerik team