I am not sure if I understand you question.
Based on what I think you are asking, I would suggest that if you have a jar that a host of other EAR's require, deploy it on the system classpath. The idea is, that if it a system wide utility library, a change in this library would have an effect system wide. It's almost equivalent to a change in Weblogic classes. Your server will need to be restarted and I think if it is system wide, you might as well put it on the Weblogic classpath.