In the past I have upgraded RichFaces in a Seam project successfully.
Seam 2.0 is compatible with Hibernate 3.3.x and Richfaces 3.3.x versions of the libraries.
I am not sure if it would be compatible with Hibernate 3.5.x, Hibernate Validator 4.0.x, ...
If you can specify the verions, others might be able to provide their experiences on library migration.
Oops, I meant Seam 2.2.0 in my earlier post.