So you have jars within a jar? Why not change ejb3.jar to ejb3.ear and deploy it? That way any jars under the .ear/lib will be by default available in classpath.
try to add the dependent libs in top level of ear, not inside of the ejb jar,
see also the j2ee 5 spec EE 8.2 Library Support
app1.ear: META-INF/application.xml ejb1.jarClass-Path: util.jar ejb2.jarClass-Path: util.jar util.jar
then it schould work :-)
what you can also try is to add the relavtive path to it lib/core.jar's