The only similarity I can see is a network of people who help one another. But that idea is orthogonal to communism. And very old: that's what a tribe is.
To use the old "steak and potatoes" analogy, if one person specializes in steak and the other in potatoes, there's capitalist efficiency there. But if there's a third-party saying "you with the steaks: you'll get those from this particular guy with potatoes. and you with the potatoes: vice versa.", that's when there's potential communist undertones.
Not that I have a problem with communism: http://news.ycombinator.com/item?id=1926047
That doesn't happen.
YC is more like a university alumni association. They foster communication between companies through events, mailing lists, introductions, etc. But, each company makes decisions independent of the larger group.