Were you able to implement compensating transaction? Can you please guide about how do you manage transaction and rollback with in process?
I believe that transaction and cancel events are currently not supported and only partially implemented. That is most likely reason why the process cannot be imported into designer. Please file jira issue for both designer that does not parse the process properly and then for cancel events and transactions.
When it comes to eclipse editor, have you selected the jbpm as process engine in bpmn2 settings in eclipse? Once you have it selected you should be able to use actor, group etc for user tasks.