Yes: the Inuit.

Probably a lot of hunter-gatherers would spend at least some of each year in a meat-heavy range of food. Inuit, athabaskans, maybe some of the old-time (pre horse) buffalo hunters. etc. etc.

Maybe some of the wealthy North West seal hunters/salmon fishers? I know they had access to plant foods but not how much they used them or if their carbohydrate intake would be large enough to make them not ketogenic.

Does anyone know more?