The leftist/Marxists I know are atheists. They see socialism/Marxism and government as a means to perfect mankind. Could this be classified as an amorphous religious worldview since it is based upon belief?
No. It could be classified as a superstition though. Religion must be a system of thought that explains to man his relationship with God and teaches how to live a moral life based on that. Religion, moreover, must have a positive track record of improving lives and attracting followers.
A mere belief, even is shared by many is not yet religion.