Better question: "Does anyone know if there's any laws/ordinances PROHIBITING metal detecting." Very rare to find any rules that specifically "allow it."
Basically, you'll find that if it's not prohibited, it's legal. With any public property, if you call locally in the area to ask, be sure you ask if "it's prohibited," otherwise, you'll be very hit and miss on answers. You can get an arbitrary "no you can't do it." without any laws/ordinances backing it up.
That being said, I did a quick search of "Ocracoke island metal detecting" and instantly found results suggesting it's off limits:
This site lists Ocracoke as being prohibited.
Outer Banks Vacation Tips - Hidden Secrets
"Most of the beach from Nags Head north to Virginia are available for metal detecting. Hatteras Island and Ocracoke Island are off limits. The National Parks Service prohibits the use of metal detectors in all the National Parks in the Outer Banks."
Here's a thread from T-Net:
http://www.treasurenet.com/forums/metal-detecting/300418-ocracoke-island-metal-detecting.html
Apparently Ocracoke island is NPS property, and it's prohibited...NPS property starts south of Nags Head
Regards,
Skippy