Board Thread:Consensus Track/@comment-4521917-20150810051444/@comment-756329-20150826205323

From what I remember the Hiden (and Shiden for that matter) were worked on by the authors with heavy involvement from Kishi. So that would make them as close to canon as possible. However, it appears that they are left up to read interpretation as well so it can go either way.

Regardless, given Kishi was involved with their creation doing illustrations for them, he reviewed them and gave the seal of approval, these books are as canon as we're gonna get for a Part III since the next Gen is Part IV so I'd vote "as close to canon as we can get"