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 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.