Yes, they are related but are not the same. Polygamy is a form of collectivism, but collectivism is not only polygamous. For example, there may be a collective of brothers and sisters who struggle together. They may or may not be polygamously married. But the polygamous family is a collective.
Comrades are a collective.
They may even think of themselves as a family. One of the principles of the Nguzu Saba is Collective work and responsibility. Polygamy may only be practiced by the unselfish and the insightful. Collectivism can be practiced by any number of folk who work for a common interest where selfishness could even be the motivating factor. Though i have lived in the country in my polygamous family.