Best practice to integrate GWT Applications/Widgets

My question is about integrating already in GWT developed applications/widgets which are more complex than the “colorpicker-demo”.

As an example: I have a module with layoutcomponents, datatable with logic for providing data, a class implementing EntryPoint, client- and serverside java code and so on. This (compiled via GWT) can be used already in a Webapplication .

Is it at least possible to integrate such a module into a vaadinapplication? If so, what is the best way to do it? Or is it necessary to completely rewrite the code?

What I´m trying to find out is how to combine the best of two worlds (GWT & Vaadin) to finally make a choice for a framework for our next projects.