I'm not an expert on the matter, but if your OW certified through NAUI, that's the card you need to show OW certification. If it's like PADI, you can be looked up by way of a student number in the event that you lost or forgot your card. The dive op can look you up to see that you are certified.
If the Peak Performance Buoyancy course is like other PADI courses, you would get a different student number on the certification card that shows only that you took the course - different student numbers for different courses. Although you may have to be OW certified to take the PPB course, the certification card does not show you are OW certified. I would carry the OW card (and take a picture of it) to be assured I get to dive.
Just my thoughts.