It's a fun idea, but I'm afraid the problem comes from the back pressure against the miner fan: To reach the same amount of cooling you'd probably have to run the fans at higher speeds, which means the additional energy necessary to run the fans would be higher than the energy that could be regained by the wind turbine. Placing the wind turbines far enough from the fans so that the back pressure doesn't matter would probably lead to the problem that the wind turbine is exposed to too little energy as to actually move.
Ahh... yeah, that makes sense. Oh well. It was just a thought.
Another thought... Why don't I see anyone making water-cooled systems for any of the miners? It takes a lot of energy to heat water... that's got to be more efficient than blowing air over the chips, right?