I recently finished the book Adland, by former copywriter and creative director James Othmer. In it, he actually asks Fenske this very question. Is advertising art? He gets a gruff snort from Fenske. Then, after some consideration, Othmer gives what I think is the most insightful answer to the question I've ever heard:
"It doesn't matter whether I think advertising is art. What matters is whether its creator does."