Coaster brakes do have heat problems on long descents. I don't know if it results in brake fade, but the heat buildup in a coaster brake will melt the brake on a long and steep enough descent. Rim brakes can also build up quite a bit of heat, but it isn't much of a problem. Occasionally letting up on the brakes will let them cool off. I don't know about disc brakes.
I don't have a problem with it, because there aren't hills around here high enough or curvy enough to warrant prolonged use of my brakes.