Ive always considered nu-metal to be the next trendy appeal to a larger audience movement within metal, and metalcore was more of a result of the hardcore punk and emo scenes bleeding over into metal that happened to find mainstream appeal. Nu-metal was the mainstream answer to the thrash scene, and along with it came the superficial tough guy imagery, the MTV appeal, etc (what was 'cool' in the 90s vs what was 'cool' in the 80s). To me, metalcore was more of the spawn of the hardcore punk and the emo scenes; most of the people I knew who originally grasped onto the scene were the emo kids who wanted a little metal in their life. I dont personally feel like the metalcore scene is the 00's answer to the same thing, as I think the scene ties to metal are too tenuous. I think metal started going more underground after the 90s, with the thrash bands of the 80s carrying the torch in the mainstream.
So to answer the original question, id say no.