Usually, by "primitivism" one means Hemingway's identification with Native cultures as more "pure" or more in touch with fundamental human values. The "primitive" becomes a haven from the modern, a place where one can fully come to know oneself.
In "Indian Camp," the primitive scene is the camp. The Indians are the "other", different than the whites, and live apart on an island. Nick's father, the doctor, is a kind of colonizing force, a representative of white civilization who has come to help an "Indian lady." In the same way colonists dehumanize the colonized, Nick's father tells him that the woman's screams are "not important," and that he "does not hear them." Later, when his father is congratulating himself on performing a Caesarian section on the woman without anesthetic, his sense of elation is tempered by the discovery of the husband, dead by suicide, in the upper bunk. The father's lack of compassion for the Indians is contrasted with George's sarcastic remark that his brother is a "great man."
There is a sense in the story that the Indian's suicide is a response to the casual erasure of humanity the doctor's treatment of them implies. For the woman, her body becomes the site of white incursion. The doctor treats her like an animal, but there is nothing she can do about it. In the face of such hopelessness, perhaps suicide is the best way out. George's disappearance at the end of the story is a similar act of desperation.