I am not sure if in your situation you can do this but:
I currently have a very similar environment as yourself but the big difference is that all the *-ejb.jar files are packaged into a single .ear file with the hibernate.cfg.xml residing in the APP-INF/classes directory (as this is considered the classes root dir in an ear).
Hibernate happily loads the cfg file through the standard new Configuration.configure.buildsessionFactory() approach.
FYI I have posted some trials and tribuation information re using Hibernate in Weblogic that may be useful
http://blogs.mit.edu/qwall/posts/615.aspx
good luck!