I find it to be unfound when reading Nietzsche, himself, and I feel Nietzsche would object to this interpretation/ascription.
Can you provide some sources here? (It would help answer the question if I knew which scholars you had in mind and the contexts in which they're making this claim.)
But here's from Genealogy of Morals: "There is only a seeing from a perspective, only a 'knowing' from a perspective, and the more emotions we express over a thing, the more eyes, different eyes, we train on the same thing, the more complete will be our 'idea' of that thing, our 'objectivity.' But the elimination of the will altogether, the switching off of the emotions all and sundry, granted that we could do so, what! would not that be called intellectual castration?" It resonates with the statement in the Preface of The Gay Science about "we're not objectifying frogs or calculating machines" (or something like that), and loads of other statements throughout his works. The idea is that cognition can never be completely separated from emotion, desire, will, context, etc. Also see "On Truth and Lies in a Non-Moral Sense," where he makes the case that regimes of truth are just regimes of metaphors that ascended to positions of power (to put it in Foucauldian terms).
He also often distinguishes between "my [his] way" and "the way" (e.g. Thus Spake Zarathustra: "You have your way. I have my way. As for the right way, the correct way, and the only way, it does not exist."), because he certainly rejected the view that the same prescriptive statements apply to everyone universally and indiscriminately. That's for prescriptive statements, but the motifs I highlighted above extend a version of that to descriptive statements as well.