Yes he was. He might have been under the Imperius curse (who knows?), but he was a Death Eater. I mean, how can you guys not remember that??? It's kind of a big deal, in book 7 - it's because Harry didn't want to kill him that he used the Expelliarmus spell, which kind of gave it away who the real Harry was, when they were escaping (in chapter 4, The Seven Potters)