I remember reading an article years ago about economic reforms in China. When asked if some of the reforms were really "socialist", a Chinese official remarked "We will try many things, and whatever works we will still call socialism". I think that many advocates of the DA/reward (a.k.a. "anhedonia") hypothesis have an equally flexible view of what reward actually means, and what the behavioral functions of DA actually are.
The DA hypothesis of "reward" is more than just a hypothesis; for many people it has become a "school" of behavioral neuroscience, which is no more refutable than Freudianism or Behaviorism.