I'm not being snarky, I just think this kind of thing fetishises indigenous groups as having some kind of deep wisdom on the basis of their ethnicity.

The whole library should stick to one system, splitting the collection in two and using two separate organizational schemes is going to make a mess. What even qualifies as "Māori literature" anyway? That wouldn't be an important question if not for the split system, but now books have to be discretely classified as one or the other. Is the classification based on the ancestry of the author, and if so, how are mixed ancestries handled? If it's based on subject, then how do you classify a book which is about the history of New Zealand generally with some percentage of it covering Māori history? What percentage is the cutoff? If all the books are organized under one scheme then these shades of gray aren't a real problem, but now they have to pick which system to put a book under, and people looking for those books have to guess how they were classified.

At least the whole system is probably digitized so there is that at least. But insofar as that solves the lookup problem, so also should it make the entire exercise of splitting the collection in two a useless waste of time anyway.