It shouldn't.  The 'java.library.path' is not for "normal system libraries".

My question was whether this IBM JAR is inherently part of the Java platform,
or if it's a regular library.

You had indicated that its location is /opt/jdk1.5.0_15/jre/lib/ibmaio.jar.
That directory, /opt/jdk1.5.0_15/jre/lib/, is for Java, not for third-party
libraries.

Since I am not familiar with that JAR as a part of Java, I questioned why it
is in that directory.

Sorry, that was in response to another comment, not  yours.  I wasn't clear.

JIm.

I keep a few command-line jars in ~/bin with eponymous scripts to save
typing:

#!/bin/sh
java -jar ~/bin/<some>.jar "${@}"

As it's a common cause of jar problems, here's a class I use to examine
the manifest without having to extract it. It might make a good addition
to JarLook:

import java.util.Map;
import java.util.jar.Attributes;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

/**
* Display the manifest of a jar file.
* @author John B. Matthews
*/
public class Manifesto {

   public static void main(String[] args) {
       if (args.length < 1) showHelp();
       else for (String name : args) try {
           System.out.println("Manifest: " + name);
           JarFile jar = new JarFile(name);
           Manifest manifest = jar.getManifest();
           if (manifest != null)
               showMap(manifest.getMainAttributes());
       } catch (Exception e) {
           System.out.println(e.getMessage());
           showHelp();
           System.exit(1);
       }
   }
   
   private static void showMap(Attributes map) {
       for (Map.Entry<Object, Object> e : map.entrySet())
           System.out.println(e.getKey() + ": " + e.getValue());
   }
   
   private static void showHelp() {
       System.out.println(
           "Usage: java Manifesto <jarfile> [<jarfile>]");
   }
}

For amusement, try and guess what happened when I (carelessly) named the
class Manifest. :-)