The metal expands and contracts at different rates than fiberglass. No matter what you do, it's destined to crack.
Your best bet for a scoop is using something like norton speed grip and bonding it on. They creating a weight/relief line so if it cracks, it will crack inside that line.
The thickness of these parts are way thicker than the sheet metal. It would require that you cut out the square holes and glass them in. I can see how you could blend it without it looking like a big lump on your hood.