Marx was indeed aware.

Lewis Morgan was an early anthropologist who had done fieldwork with Native Americans in the 1850s (including with hunter-gatherer tribes such as the Crow). Marx was familiar with Morgan's work and, it seems, intended to write about it; to quote Engels after Marx's death:

No less a man than Karl Marx had made it one of his future tasks to present the results of Morgan’s researches in the light of the conclusions of his own — within certain limits, I may say our — materialistic examination of history, and thus to make clear their full significance.

Engels took on the task and produced On the Origin of the Family, Private Property, and the State.

However, while Engels's book is a very interesting read, it (in my recollection, it's been a while) doesn't stress the "primitive communism" aspect of hunting and gathering.