I don't see why it wouldn't help protect it, just as it would the paint. But, not for very long.
Let's say a typical wax lasts 3 months, D151 contains a wax, although not a dedicated wax. But for arguments sake and the fact I haven't personally used it, lets say you would get 3 months of protection on your headlights.
So yes, it would help, but not permanently seal or protect. Use a dedicated coating or sealant for longer protection. Just my 2 cents