I can now understand your approach and appears to be good for me. I'm running jBPM within a similar environment (JEE 6/JBoss 7). I guess my CDI beans can be injected as you did with your components as global variables and then invoke their functions from a script task avoiding writing java code within XMLs.
Going back to tasks; do you know what is the actual difference between Tasks and Service Tasks?
Thanks again for sharing your valuable experience!