The site is indeed relatively worthless, and I doubt anybody at all is paying them a high cpm in anything. Thats the whole point, to turn low cpm into somewhat higher cpm, in the long term by capturing more of the revenue stream.
Is it fool proof? No way. Facebook or whatever, could risk losing their investment in whatever company they bring up, and also lose the opportunity cost on whatever ads they could be selling instead of sending to their own child company instead... But does it stand a better chance at making more money in the long run compared to magical BS like social graphs and social ads? Yes, I definately think so.