The Power of Z!
Hala himself stated in SM09 that Totem Pokémon rarely hand out Z-Cryatals, which implies that they sometimes do. After all, Totem Pokémon are working with the island guardian deities, and it's clear that Totem Gumshoos rewarded Ash with Normalium-Z because Tapu Koko wanted it to.Well, it was sort of weird that a Darkinium Z was a Totem Pokemon's possession...and the fact there was a Dark-type Totem Pokemon at all. Does this either imply not all Z Crystals are officially handed down by Kahunas an anyone can hand them over, or other Totem Pokemon of different types that were never a thing in the games rule out a Kahuna from appearing? Then there's the fact we don't know how the Ultra versions will affect the rest of the anime since the anime adapted to new enhanced versions late into their episodes.
I think it's still a safe bet that all of the Kahunas from the games will appear in the anime, and Hapu and Nanu are no exception. There is no reason for them not to appear. Yes, it's possible that one or both might not have a role in USUM and thus not appear in the anime, but I think it's way too soon to jump to conclusions or make any assumptions like that. For now, it's safer to assume that all of the Kahunas are going to appear in the anime