Amtrak's P30CH's had two aux diesel engines for HEP. Powering freight car equipiment from a locomotive while technically feasible, is not too practical. Among other things, to avoid voltage drop over distances longer than a passenger train, the current woulld have to be greater than 480 volts. Equipping the car fleet with the necessary cabling is a significant cost and the main reason it will take years to phase in ECP brakes. Same would apply to equipping locomotives. If one thought to limit the fleet of cars and locomotives to a limited scope of operation, then you lose flexibility (or have to hunt around for the proper equipment to make up a train set.)