We have deployed our JBoss Seam 2.2 application on JBoss 5.1 with PostgreSQL as the database. It makes use of EJBs, JPA (Hibernate), JSF (Richfaces and Primefaces), Servlet
The short answer is yes you can migrate your Seam 2.2 app to JBoss AS 7.
The main challenge is going to be classloading because of how class loading is completely re-architected with AS 7.
Instead of me going through all the steps here I simply want to point you to the official documentation of how this was done on one of the sample apps (Seam Booking application). It provides a step-by-step guide on how you can migrate a Seam 2.x app to JBoss AS 7 and also points some of the issues you will face and how you can handle them.
The guide is located here.
Other useful references
Good luck!