I figure now is as good a time as any to actually start posting instead of just lurking
Just my 2 cents, as an athletic trainer that's been in the business for a while (including several years with hockey teams). In very simplified terms, the two biggest factors in determining return to play following an injury is, 1) can they worsen their current injury to the point of long-term/devastating effects, and 2) can they protect themselves. Just going off of mechanism and the timeline the Ducks posted, Fowler's injury definitely looks like an AC sprain. While he could "gut it out" and play without a whole lot of (relative) risk to the actual current injury, the biggest issue I've come across with hockey players and AC sprains is that they do not have the range of motion or strength to protect themselves out there from additional injuries (incidentally, they are not all that effective, at that point, either).
I obviously can't speak for the Ducks' athletic training staff, but that's just been my experience.