I just spoke to someone at the USVI Dept. of Tourism. They told me that they do accept a positive antibody test for entry via ferry from the BVI. Great news! The only caveat they mentioned is if the BVI requires an exit test irrespective of your destination's requirements. Anyone wishing to confirm can call them at 1-800-372-8784. It is my understanding that all the BVI requires is proof of entry clerance from the USVI portal. I got a busy signal the first couple of tries, but when it rang through they immediately answered.