I have made a complex models structure in django. I had planned to render this structure using GWT, but with python the option to communicate whit it are: - using JSON and
I think you need to make your decision based the usual factors: how much time do you have to develop your app, and what are the best set of tools to get the development done in that time.
If you have made the decision that Django is your server-side framework (which is my favorite choice) then it seems pretty clear that jQuery, Dojo, etc. are probably going to integrate easier with your Django.
On the other hand, if you have more time and especially if you could open-source the Django interface parts, then it would be very cool to write some code that could hook into Django internals and generate the necessary Javascript to seamlessly interface with GWT and not violate DRY.
So in short, if you have to get the app done go with jQuery. If you have more time and want some kudos then develop a nice seamless library for Django that will render the proper HTML + Javascript from Django models and forms that will integrate with GWT.
Just my opinion :)