Hm I have to try it first, however, have you tried to write the boundary event by hand and to import it into oryx? Would be interesting to see what Oryx does with it, especially when you save the imported BPMN again with Oryx.
According to the documentation, boundary events are not yet supported and are supposed to be written by hand.
5.4.2.2. Throwing error event
Error handlers can be specified using boundary events. This is however currently only possible by doing this in XML directly. We will be adding support for graphically specifying this in the new BPMN2 editor.