It won't directly make a difference, and indirectly might slow it down.
Think horticulture. When you create a layer and sever the flow of auxins down to the base of the trunk and the roots, it is the mass of foliage (and specifically the growing tips of the branches) that is creating that auxin flow. The way to get roots to form faster is to allow the tree to grow strong foliage before you conduct the layer. But there also comes a point where more auxin isn't going to be more effective. Once you reach that saturation point, the tree is being triggered to grow roots at the girdle and more auxin (either from a natural or artificial source) isn't going to accelerate things.
The roots in this case are primarily there to provide water for the foliage. If you start reducing the existing roots, you may stress your foliage or cause it to crash. It would be a little like turning your tree into a big cutting. The value of an air-layer is to keep the roots providing water, so that the foliage remains strong and continues to pump out auxins. (The roots will also trigger bud development below the girdle, but that isn't really a concern in the case of a ground layer).
