IMO if a Saison recipe calls for wheat, you need wheat. It's simply a very common ingredient in a Saison. What you use for wheat is what you have, although I've read that a few different types can taste different from each other.
In the heydays of Saison the farms making them would use whatever they had, and ferment them at room temperature. There isn't really any hard and fast rule on what they taste like, but some commonality would occur.