I've been playing around with seam-security in a tomcat6 environment using maven as my build tool. I opted to use picketlink's hibernate identity store implementation. It appears that the 1.5.0.Alpha02 version of picketlink-idm-hibernate.jar is not compatible with the version of Hibernate that is served up by the seam3 bom (3.6.0.Final). It serves up a class cast exception on line 520 of HibernateIdentityStoreImpl.java. The good news is that the fix is easy. Change the cast from Integer to Number on line 520, build and install the artifact into your local repository, and you're off to the races.
I created a patch, but then I couldn't find anywhere around here to upload it. Because the fix is so simple, I figured I'd just drop in and mention that somebody on the seam security team might want to look into it. I'm a Seam noob, so there's a fair-to-good chance that I'm missing something.