Are there any major advantages to using Java 6 over Java 5 for the development of web services? From what I've read, JAX-WS can be back-ported by adding its libraries, and the richer stacks, such as Metro, support Java 5.
Are there any features in Java 6 that we wouldn't be able to get via libraries in Java 5? Can the new security features be imported just as readily? Are the available, stand-alone libraries for 1.5 maintained?
Java 6 ships with a version of the JAX-WS reference implementation, but that's about the only relevant difference to Java 5. I'd even regard that as a drawback, because that version is already obsolete. So, yes - Java 5 works just fine, and it's all you need to run Metro, including WS-Security.