"run" is an exaggeration, while of comparatively high torque, they are low velocity engines (to contrast with other undead of English lore such as moor wraiths which are of higher velocity but near zero force). As in all matters, culling productivity from undead requires balance. Modern engineering could certainly harness zombies for productivity, but it is along the lines of a mule, slow, steady ... the type of thing that can move water up out of a well.
The project is a simple one, chain the zombies on a wheel (like a mule) and have a good number of grain fed humans working in shifts as the carrots. There needs to be a lot of humans as the work is yucky, the zombies smell bad, and there are work hazards should one get dizzy and faint.
IN this model we are simply converting solar power (that which made the grain) into mechanical power provided by the zombies. Should carrots fall then a short spike respiratory CO2 emmissons would occur.