To add to Rick's comments, most etching primers use some form of phosphoric acid to give the paint some bite. However, some epoxies are not compatible with these acids and it will cause adhesion issues down the road. If all of your materials are from one manufacturer, you should not have an issue, but it would definitely be adviseable to check before going any further. I also use a direct to metal epoxy, no etching required. If your metal has been blasted, that is a good abraded surface for a DTM epoxy, where etch really isn't needed.
Regarding the black EDM paint, some will just scuff it up, and epoxy over it. Some will strip this coating off, and start from bare metal. Given its source from overseas and uncertain prep, I personally feel more comfortable stripping to bare metal, cleaning and prepping from there. Others may disagree, but rework costs more when you are doing work for someone else. I'd rather be sure of the substrate and adhesion. Although you would likely be safe with either.
