Kevin,
If the widgets and simple and static, coding them in GWT may not give you a lot of benefits. If the backend language is Java and you are looking for utilizing the same language for both backend and frontend, you should seriously consider GWT. Otherwise, straight javascript plus html5/css3 may suit you better. GWT is good for complex one-page web applications. If you have thin and brainless widgets, GWT may seem overkill. Also, GWT has its own drawbacks. First, it does not yet support all the html5/css3 features. Second, and this might be more important to you, Google is currently focusing on developing Dart, the GWT replacement. With the focus shift, the missing html5/css3 features may not get to GWT any time soon.