Loading a Jar file in Oracle with loadjava, problems

When trying to load a .jar file with the command

loadjava -v -u username/password -r .jar

I get a bunch of errors like

resolving: class net/sf/hibernate/AssertionFailure

errors : class net/sf/hibernate/AssertionFailure

    ORA-29534: referenced object
AUTHOR.net/sf/hibernate/exception/NestableRuntimeException could not be resolved

The class NestableRuntimeException is in the jar file.

I can load a simple jar that was compiled with the oracle native jvm ($ORACLE_HOME/jdk/bin/javac), but when I'm trying to import jars I downloaded from the internet, I get unresolved errors.

Questions:

1. Do I really have to import everything in source code so the oracle JVM compiles it itself?
2. If I CAN import jars, do they have to be compiled on the same exact version (e.g. if oracle runs 1.4.2_02, I cannot use any jar compiled on 1.4.2_03?