Not that we know of.
i tried using JpdlXmlWriter from JBPM once.
It worked creating a xml from a processdefinition read from a xml file.
It didn't work creating an xml from a processdefinition read from my jbpmdatabase.
that's why I said: Not that we know of ;-)
It would be nice to have that. It would help a lot when you are creating Process at runtime and you want to see in an xml format what you are creating. I hope jbpm people consider implement it, could be at free time :).
This is not on the todo list, but feel free to donate some of your free time and contribute and maintain a working solution.
Our personal free time is limited, very limited