Thus far the only thing that's canon is that small part of the Script, which I actually have forgotten about. The gameplay itself can't possibly be canon as it's only based on the Keyblade War (and the presence of Emblem Heartless already contradicts the main timeline canon since they are only manufactured at a point of time between BbS and KH1), but elements of its story, such as the Foretellers and Chirithy, may very well be canon.