Since 6.1, we have not been able to export our custom visualization component in any format within JasperServer. We have now upgraded to 6.3, but still see the problem. I had entered a bug in the professional support portal long ago, but was advised to ask for help here since it, despite the fact the feature is displayed within official Jaspersoft documentation, is only supported by the community. Note that we have been able to successfully render the custom visualization in a report in both Studio and JasperServer environments as well as embedded as a dashlet within dashboards.
casey (iOffice ~ email@example.com)