For any steel or tin part that needs to be re-chromed, I have always removed rust down to the bare metal before I take the parts to the re-chroming shop. Sometimes this can be accomplished by blasting the rust off using a workbench grinder motor with a wire wheel (using the wire wheel). Ugggh, mine gets a lot of use. So the wire wheel can become dull, but if you take the wire wheel off the motor shaft and turn it around, it will work like new again. If there is pitted rust, the part might still be salvaged by carefully grinding down to bare metal using a Dremel rotary tool with a little grinding stone attachment, but then the metal needs to be polished down smooth. Regardless of how you bring it to them, they will still dunk the part in acid to clean it and polish it down. There can be no fingerprints and even the natural oil in your hands and fingertips must be completely erased prior to chrome plating. That's why they always clean it first.
Ole Don.... are you saying that you paint primer over the part with the intent to have the plating over the primer???