Is Cosa Nostra a non-profit? The question doesn't make sense. It's a category error.
A non-profit is a corporate legal structure. An unregistered organization could be a cabal, a gang, a syndicate, a fellowship, a religion, a movement, a private club, or something else.
The intent is still important. While from a legal point of view a terrorist cell cannot be registered as a non-profit, it typically spends whatever funds it can secure to further its political goals, not on increasing the wealth of its owners or participants. A typical criminal band though is a for-profit entity.