I think a 3rd party arbitrator isn't a terrible idea, although if the actionable clause is "against WotC's values" then I'm not sure who would be a better judge of that than WotC.
Objective standards are fine on paper, but they are always going to be too soft for some, too hard for others, and fail to account for everything. Not to mention inviting loopholes and tip-toeing of lines on sheer principle. In practice, such standards are dicey at best, and horrifically arbitrary at worst (lookin' at you, MPAA).
That's the thing I think most people are missing about this. These are Wizards' toys. And their "morality clause" is really about their values. It's not about whether a work measures up to any objective or subjective measure of "appropriate" or "inoffensive". It's about whether the work (or the primary activities of the person behind it) promoting, existing alongside neutrally, or actively working against said values. If it's their values, why shouldn't they be the judge of who measures up?
I think there's a tendency to view this as analogous to the Hayes Code, but that's absolutely the wrong analogy. The actual analogy is a politician you hate playing your song at their rallies.