Unlike most plants, hydrangeas don't have the ability to close (or partially close) their breathing holes (stomata) when they run out of water. This means that if they wilt, they will wilt very quickly. While hydrangeas a great for shade, they will be a high maintenance plant in dry air, and I wouldn't think they would be very happy growing in dry desert conditions.
Sorry I can 't recommend anything for you, Joe. I am not that familiar with southern climates.
