I bet you would probably be fine with either category. I was trying to see if I could find Troegs Nugget Nectar listed as a commercial example anywhere. I couldn't. Troegs defines it as an Imperial Amber. American Amber has Troegs Hopback listed as a commercial example. I would consider it to be the little brother to Nugget Nectar.
I actually just kegged a beer similar to this. I purposely just brewed a hoppier nugget nectar-like style beer. I call it a "Hoppy Imperial Amber" lol.
I probably would go with American Amber.... but It's a tough one. It would probably fit in both Red IPA and American Amber.