There are a lot of BPMN2 Editors on the market, even open source.
But there are only a few editors usable for jBPM since most of those editors store the BPMN2 proceses not in the standard XML defined by BPMN2 but in a propriatory format, some in an XMI format.
Some Editors produce correct BPMN2 XML files, but jBPM is NOT fully BPMN2 compliant.
The BPMN2 grammar does not define, that elements must be defined prior to their refence. jBPMN assumes that all elements which are reference by a BPMN2 element are already defined. That assumption is wrong and not BPMN2 compliant.
We found that on the OSS market the most reliable and feature-rich editor is the editor Yaoqiang BPMN Editor: http://bpmn.sourceforge.net/