My RotorPros rotors on my 03 aren't powdercoated but they are painted black with a high heat enamel. They came that way when I bought them. Doesn't hurt anything. I'm sure it helps prevent corrosion/surface rust to some extent.
I believe the Centric Rotors on TireRack come treated on the hub and outer area.
12 Black GT500 SVT PP l VMP TVS l JLT123 l O/R X l 28x11.50Rx15 M/T Street R's l BMR Suspension l Recaros
03 Sonic Blue 3.8 / 17 Magnetic Fusion Sport 2.7 EB