I'm fairly sure -- on the basis of what I've heard -- that jBPM 5 will be integrated with Switchyard, which is basically the new jBoss ESB.
See http://www.jboss.org/switchyard for more info!
(In fact, they've already started (and done lots) on jBPM integration: https://github.com/jboss-switchyard/components/tree/master/bpm )
As for the "old" or "current" version of jBoss ESB, I think it's a better idea to look at Switchyard if you don't already have jBoss ESB setup.
Marco