Hey,
I have used Spring and GWT.
Basically I liked the notion to isolating front end and back end, so I was using GWT as front end and Spring with RESTful services as back end.
This way you can have loose coupled GUI.
And as far as spring MVC is concerned, one may achieve it with little changes(complex though).
And if you like to use plain spring and hibernate with GWT, you may use it on server side. I don't see any problem on that side. After all they are
java framework with configuration.
P.S : you can check out smartgwt api for such purpose. It may provide support for ORM.