got it to show up, but I did several things so not sure which one did it...
1) renamed my work item descriptions file to end with .wid instead of .conf.
2) created a new flow diagram which created a file ending with .rf, when this opened in the designer, my domain specific process was in the palette
3) closed the .rf file and went back to my already opened .bpmn file, the new process was not there
4) closed the bpmn file and reopened it, now the new process icon shows up
Another step that helps is to do a Build All. Maybe the writers of the documents assumed everyone turns on auto-build. That seems like the most consistent way to get an update to show.
However, though your icons may show up in the palette, when you create an instance in your workflow, you might get a little red square instead of your icon. The only way I've found to fix that is to close the project and exit Eclipse. Upon restart and reopening the project, when you open the bpmn file... voila, the red square is gone and the correct icon is shown.