All the A/C in Fedex color are own by FDX, and lease the A/C to different feeder operator.
4 Operators for the ATR : In The USA : Mountain Air Cargo & Empire Airlines, 1 operator in Canada & 1 in europe ( Do not recall the name ).
C208 in the US : Wiggins, Mountain Air, Baron Aviation, Corporate airlines, Empire Airline,West Air & CSA ( Own by Airt who also own Mountain air cargo ).
FDX also uses other operator as feeder A/C ( Those A/C are not own & are not in FDX color ). As an example, IBC airways & IFL are used in Miami by FDX to go to Mexico & the Carribean.
Hope this help.