In the USA they are classified as buildings. They even blink at the top and bottom of their circular flight path so that they look like radio towers to airplanes. As such, they are not regulated as aircraft, and for better or worse, have freedom in how much systems redundancy they add, how rigorously their software is tested, etc... In Europe, similar systems (i.e. like the one from Ampys) are regulated as planes, and have to use all aircraft certified stuff.