Thematic Mapping API returns KML as string object in JavaScript. This
string can be parsed by any application supporting the KML format. You
can not use the GGeoXml class of Google Maps API as it requires the
KML file to be fetched from a web server and not from dynamically
created string. I think the reason for this behavior is limited vector
handling in current web browsers - Google Maps is rasterizing the KML
on Google servers before it's displayed to the user.
It is possible to use a third party parser like GeoXML which allows
you to parse KML from a string object (parseString method) instead of
loading an url from a web server. I've not tried GeoXML with Thematic
Mapping API.
http://code.google.com/p/geoxml
Bjørn