I think they should. Wikipedia follows the Open Source ideas, the license being first GFDL, later CC-BY-SA. These licenses are fully in the idea behind open source, the only thing is they have no source (as they aren't code). Question about Creative Commons was asked before, so I think we can count Wikipedia as an Open project, as it has a license that falls into our already established scope.
EDIT: I would apply the same to other Open Knowledge projects, even if the license is open shareable, but not fully open source (like CC-NC and CC-ND licenses), because the top-voted answer to this, says these licenses should be included. Only because they are applied to knowledge, they shouldn't be out of scope.