Did some more digging and stumbled upon another older thread where BenFrantzDale says “Those overlaps will be drawin twice but in my experience it is not a problem. You will get a little resin savings.” http://forum.formlabs.com/t/sharing-base-of-2-parts/9457
So it is confirmed that it will print that area twice. It would be a small improvement in resin tank longevity if it did not print that area twice.