Ryegrass is fine up to about 90 degrees--if it is well-watered, yet not too humid at night. Brown patch and gray leaf spot are bad in warm climates--especially where the temps get over 70 at night. Of course dollar spot, red thread, and rust can be anywhere. Really, I think rye should not be sold south of Richmond, except as winter overseed for Bermuda. Try showing him a map of adaptation for ryegrass from a seed compan's literature or website. He will probably give you a call about mid-June.
Maybe this map might help: