Some of the early adopters of MESA were in Florida on warm season grass. The use there has grown steadily and substantially so I am inclined to believe that you would be fine in TX as well.
There is always a chance for turf injury under extreme conditions of heat and or moisture stress. However, you can use MESA well beyond the point at which you would cease to use granular ammonium sulfate, and I think under any condition that you would use feel comfortable using an SCU blended product. Because of the homogeneous nature of MESA foliar contact of AS will be negligible. Still, you might opt for dry foliage during the application as an extra precaution if the temperatures are extreme.