Dan,
Have you seen the nstomcat module available at http://www.ss.pub.ro/~gaburici/nstomcat/?
This embeds a JVM in the aolserver process and runs Tomcat in the JVM. The author has notes and results for use with a few different JVM's (1.3 looks good). I know your nsjava project has different aims, but the basics of a JNI connector are the same so I thought I would point it out.