Most (if not all) people have reported that their health insurance card has sufficed to get in, however, this is a personal decision based upon your comfortability with paying for staying an extra ten or so days in a government approved hotel for quarantine (assuming you don't own a boat or lodging on island), just in case you test positive when preparing to return to US.

The U.S. and USVI also accept a fast antigen test as long as it is proctored (ex: Abbott BinaxNow, but there are a few others out there that meet the requirements.) One of the benefits of a proctored rapid test is in case you test positive you can do it again. If you take an on-island PCR test, and test positive, that is it. Enjoy your extended stay.