Zombies of Melkor, Arise!

[Inziladun]

Aulë the Vala committed a sin in the vein of Melkor (though with better intentions) by presuming to 'create' a race of beings, the Dwarves, outside the design of the Prime Creator, Ilúvatar. He received a stern rebuke for his folly.

Why dost thou attempt a thing which thou knowest is beyond thy power and thy authority? For thou hast from me as a gift thy own being only, and no more; and therefore the creatures of thy hand and mind can live only by that being, moving when thou thinkest to move them, and if thy thought be elsewhere, standing idle.

Silm Of Aulë and Yavanna

Here is the issue: Why could Morgoth not have made a race of beings like Ilúvatar described, fundamentally mere 'hands' to do his will? They might seem to be excellent troops, something like the battle-droids of the first three Star Wars movies. What they lacked in intelligence and creativity could have been balanced by their unquestionable loyalty and potentially incredible numbers. Additionally, they would not have been subject to some of the failings of the Orcs, such as their sometime cowardice and greed. I'm not suggesting he might have made soldiers like in the place of Orcs, but they could have been a powerful supplement to the might of Morgoth.
Did those thoughts simply never occur to Morgoth, or was he happier with the Orcs, overall?

[Ibrîniðilpathânezel]

The trouble with a zombie is you're foreverlastingly having to tell it what to do. Go here, go there, do this, do that, etc. In massive armies, there has to be a certain amount of ability to act and think outside the parameters of a specific order (which can't be too complex, because the zombie can't think for itself). Taking something already possessed of intelligence and the ability to think as an individual provides a higher level of functionality, which can then be corrupted and debased until a desirable level of ability and disability is achieved, which can then be reproduced.

Melkor clearly needed a higher level of ability than he had been given in his own creation in order to fashion beings that met what he considered the desirable combination of native subservience and independent functionality (remember all the time he spent seeking the Flame Imperishable). The creatures he could make, ala Aule, just would not have been up to the level of ability he desired. Zombies might make reasonable cannon fodder, but they wouldn't have been much to boast about, and like all despots, I think Melkor wanted the satisfaction and ego-boost of knowing that his armies and slaves either worshiped him or feared him. Zombies can't really do either.

[Legate of Amon Lanc]

There has been at least some idea that the original Trolls were like that. I think the matter of Trolls was never completely cleared (Tom, Bert and William were certainly not guided by Melkor, or Sauron, for that matter), but there was always this somewhat shady concept in the background. I don't have the quotes at hand, but I recall that Tolkien said about trolls (trying to recount the quotes as well as I can remember them, it is basically word-to-word) things like "it seems clear that they were made (as opposed to "created") by Morgoth, although it is not known from what". Likewise, there was something that Tolkien said which implied that the turning to stone effect was a result of the fact that the Trolls didn't have a "real" life of their own (I think it was in some of the books, like Sil or UT or maybe even in the appendices to LotR).

Now my personal speculation on how to put this together - maybe it was not that they would be directly controlled by Melkor, but they would be indirectly driven by his evil will, as long as he remained aware, in the corner of his mind, that they exist. Or not even that, they would be just manifestation of his evil will and intent. Not sure if you can follow me, it's hard to explain, but the idea is very simple. Like, imagine a person (in some alternative universe) inventing a fork. He made the fork with intention to be used for eating. His lifetime goal is to make all people eat with something else than their hands. And as long as he remains thinking of that goal, the forks will be used for eating. Okay, that was a very bad example, but hope it can at least shed some light on what I have in mind. Morgoth's intention was to cause evil. He made the trolls as instruments of that evil. He did not need to focus on every single troll at each moment, but as long as he was focused on causing evil (which he was basically all the time, that's why the trolls were active all the time and not really "shutting down" at any moment, except for the sunlight - I guess that's an important thing too), the trolls would be walking around the world and causing evil, as there will be this "evil intent in the air" still. Hope it's understandable the way I said it.

[alatar]

Aule's Dwarves, before they were endowed with 'souls' of their own, were like brain-controlled robots. Think that it was said that whenever Aule would look away from them, they would stop and await new commands.

Surely Melkor would need to think elsewhere at times during a battle, which would leave his robots vulnerable.

That said, what about the whisperings of Saruman? Again, I don't have the quotes, but wasn't it said that, even when far away, some still heard the whisperings of Saruman in their ears, compelling them to do his will?

Turn that up a notch with Melkor, and you could have zombies.