as i see it:
Rules (e.g. to decide which transition to take runtime) go into the rule engine. No overall process definitions
Workflow (human interaction) go into the BPM (JPDL!!, not BPEL) engine
ESB takes care of integration (file, ws, b2b messaging), service orchestration based on e.g. BPEL, transformation etc
Would anyone happen to have a specific example showing details? From a high level, it all makes sense. Devil is in the details :(
the jbpm examples contain a workflow/rules example. the esb comes in when e.g complex external services have to be called. an example of that has to de done by by yourself for the moment, but don't hasitate to post an example on the wiki.