Is there any official documentation affirming Java 1.5 and JEE5 support by Google's GWT (2.1)?
I couldn't find any specs which parts of the Java language are officially supported by GWT. Are there any statements by Google? So is it possible that all parts of the Java language are supported and translatable in JavaScript? The only thing I found on the GWT website is: "The GWT SDK provides a core set of Java APIs and libraries.." but no further declarations...
The page Coding Basics - Compatibility with the Java language and Libraries should answer your questions.
If you want a breakdown of the java packages and methods that are supported, you can go see the JRE Emulation reference page.