Yes, we're still using GNU Classpath. Open JDK support is not yet ready.
I'm not sure if there's enough interest in JMX by somebody in the Jikes RVM community to warrant further work. It's been a long time since anybody asked for it.
Personally, I don't need any of the JMX beans that I mentioned above. I've worked on JMX because I want to have an implementation of the threading bean features so that I can use JUnit timeouts without getting an UnsatisfiedLinkError (see RVM-692). I've merged the rest of the JMX features because the code was already written and it just doesn't make sense to let it bitrot any longer.