Yeah, I saw articles on systems like you are describing. It's trading off efficiency for simplicity. It's just a lot more efficient to transfer the heat from a liquid to the surroundings than from air, and liquid holds way more heat per unit volume so you don't have to move it as fast.  Keep in mind that you'll need to push around 200cfm of air per miner through your pipe, so you'll need very large pipes and an air system that can handle very big static pressures. So for the scale you're talking about, I think the liquid one with a heat exchanger is probably going to end up simpler in the end. But in my opinion, neither will be as inexpensive or as simple as an evaporative cooling system.

But I'd love to see the results of a test. Just set up a single air loop with a single miner, and bury 50 or 100 feet of 6 or 8" pvc.