I notice that you are using Java 1.3.1 as supplied with your Websphere installation. Try a more up to date JDK from Sun (e.g. 1.4.1). This can be installed in a separate directory and you can build your Inline::Java against that. Since Perl is going to be running your Java apps, you can use a different JDK to the version being used by Websphere.
I can't really test this since I don't have AIX but it could be worth a try.