The integration with JBoss ESB allows the ESB to start a process and respond to service requests from jBPM. It does not restrict jBPM functionality in any way. You should be able to use any tools supported by jBPM for this purpose.
I will be presenting a demo at JavaOne in a few weeks and intend to show seam/jBPM/ESB working together. I will be using the seam task management integration with jBPM to drive the process through to the ESB.
And it will be recorded and available online at a web site near you soon afterwards :-)