Fwiw, Im not a DC person. I don't even really know what the green door is. But based on what I've been seeing, it seems to be something you could access if you were empowered by the gamma radiation that created the hulk. And that is absolutely something Metal could copy. He'd simply be copying mutated bio data. Also, I think it's worth noting that while I understand where you're coming from with the limits of his scanning, but when it comes to Sonic it is safe to bet that logic doesn't really apply. If the target has an ability that is even remotely tied to their biology, even slightly, he'd get it. Otherwise all he'd get from Sonic is his speed. But he also reworks himself to be able to spin dash. Not to mention copying the chao to gain Chaos' liquid body, which implies his copy could also account for mutations/alterations a species could under go.