I feel that regardless of what is taking place to produce that output, some type of computation must have taken place. Yes, connectionist-style info processing is computation. Not as it is dogmatically defined by the computationalists, but in a slightly broader meaning. Computation can be defined as the act or action of calculating mathematically. PDP networks are definitely performing mathematical calculations even if they are not following explicit rules.
Summation just is mathematical computation.
In certain ways, PDP might give the same output as a digital computer would. I think an important question is raised about the necessity of internal symbolic representations to cognition. While the connectionist explanation seems intriguing to me, I understand the objection of the computationalists. If I was pinned down, I'd say the criticism does not invalidate the PDP model.