The answer is...it depends ;-)
JBoss supports a variety of classloading scenarios. Each will have an effect on the 'structure' of the repository. Typically, the the JBossClassloader architecture results in a 'flat' namespace where you have the UnifiedLoaderRepository and *all* UnifiedClassLoader3 instances point to the same repository. Again, this can be changed to support different scnearios.
See the following pages from the Wiki:
There is quite a bit of information on the Wiki on classloading, so this is just a start.