Absolute humidity will almost always be higher at 30C than 0C, though relative humidity can vary and that is what would cause an issue for condensation. If it's really muggy you might be worried about that, but mining equipment will almost always be hotter than the surrounding air you shouldn't have many condensation issues unless the conditions are extreme.

Not saying you couldn't put them in a place where you could run into issues, but if your gear has a low enough ΔT that it is able to run in a comfortable range with 30C (or even higher) ambient the benefits of the colder climate wouldn't come close to outweighing paying 67% more in electricity costs.