Regarding the class loading behaviour of different versions of the app server, I recommend posting on the app server user forums.
Regarding dependencies of JBoss Cache, you'd need:
That is, unfortunately, the bare minimum (for JBC 1.x)
Tried to move to JBossCache-2.0.0CR3 + Hibernate 3.2.5GA, but they do not appear to play nice together:
Hibernate's in the process of putting together a cache provider for JBC 2.0. I know that the EJB3 guys are also doing one for JBoss AS 5. You could write one yourself - it is dead simple. Just look at the existing TreeCache/TreeCacheProvider wrappers in Hibernate and write your own.