To me this seems to be more of a marshaling problem than something with AMQ. I have not used Json with OpenEdge but it works just fine with Camel:
Also if you post the json message we could take a look to see what is wrong with it.
I have found the problem in web/MessageServlet.java. When I receive the return response the Content-Type is fixed set to "text/xml".
Regardless if I put my own Context-Type as message property to "application/json" this is overruled by MessageServlet.java.
- Jan Douwe