Interfaces for Views and ViewModels are not required by Unity to be able to inject them. Interfaces for Views or ViewModels allow you to test them in isolation by creating Mock classes for the
dependencies between them. If you are not doing TDD nor mocking dependencies, there is no need for you to use interfaces.
In the source code and the documentation, the ViewModel (in M-V-VM) is referred as the
Presentation Model, and they are basically the same thing in the WPF/Silverlight context.
That said, you can check the Reference Implementation or some of the QuickStarts to see examples of using Presentation Model with Prism-v2.
Please, let me know if this helps.