Electric power is well suited to driving the huge wheels of a 4x4 monster truck, great low end torque and wide power band. The problem might be battery weight - monster trucks are basically lightweight space frames with low unsprung weight pushed by a big block V8 engine with a flimsy fiberglass body over the top of it all.
With how massive the wheels and tires are, maybe hub motors with batteries packed in their centers could work. I don't get the impression that monster trucks strive to minimize unsprung weight, the tires are wrecking balls.
