McGonagall Likes My Quidditch Skills
So I agree with everyone who said he probably wouldn't have used Dementors. If he had, they wouldn't have been used ever again to guard the prison. I like the idea of Voldemort not being able to cast a patronus, but could his happy memory being killing someone? It's a scary thought, but it seems to fit Voldemort. I agree that I'm pretty sure he used Inferi, probably at least a few giants (I kept wanting to type dragons), werewolves. Like everyone else, I'm not sure what Hags do or if ghosts could exactly help him or would even go to his side. Trolls are kind of stupid, but he may have used them for somethings (though i'm not sure what). Some Vampires probably went to his side because I feel like they would be even more feared than werewolves because they are dangerous all the time, not just during a full moon. But also at this time Voldemort had many more Death Eaters. He may not have needed those creature reinforcements like he did in the second war where actual D.E numbers were lower.
This is a very good point. But then we come back to the original question: would Voldemort have used them at all, and what for? I can honestly only think of gathering information, but that doesn't seem probable. I wouldn't trust a ghost. What we've mostly seen from ghosts in the book is that they just drift around and don't interact with people (Nearly Headless Nick and the Fat Friar being exceptions--all ghosts are different). If a ghost started getting nosy, people would get uncomfortable. They just don't seem reliable or solid; they're wanderers and most probably wouldn't trust someone like that with any kind of important information. However, a ghost might be given the task of turning invisible and sneaking around and eavesdropping, checking to see how things are going along in another place and such.
Originally Posted by Apollonious
Actually, I think that because their minds are still present, they could be controlled through Legilimency or an Imperius curse. I mean, other kinds of things, like Basilisks and Lupin's "waddiwassi" spell, can affect them (Although that was technically on a Poltergeist, I think the principle holds true). Based on canonical evidence, it's actually pretty probable that Voldemort could control them. Not just through Legilimency, either. He might use a Cruciatus curse, or other means of physically controlling someone. It probably wouldn't be as effective on a spirit-based being as a human, but it would work.
You know, a long time ago, I tried to think up a fic about exactly the same thing: a war with dragons. I can see this tactic work. I think I'll steal it.
Originally Posted by Apollonious
On the use of dragons: I actually quite like the idea of Voldemort (or someone - maybe in the Middle Ages) using dragons in a war. The image I have in my head is rather like dog or cockfighting. Voldemort (his servants, actually) would starve the dragon and make it as vicious as possible. They would keep it in a cage, I imagine, very cramped, with the metal enchanted to withstand very high heat. Then, during a battle, they would point it in the direction of their enemy and open the cage. They wouldn't need to control it, exactly, just get out of the way.
Back on track, this probably would work. There's just the obstacle of smuggling the dragons out--but didn't Hagrid get the dragon's egg in the bar from Quirrell/Voldemort? Those are supposed to be highly protected. And so breaking in could be easy--getting huge beasts out would've been harder--but perhaps not. Cast a few spells on them--wasn't there a spell that could stun dragons, especially between the eyes? The Conjunctivictus or something. Make them invisible, I suppose...Voldemort was powerful enough, and if he didn't do it himself, he could've had some of his Death Eater troops do it (which I doubt he would have).
Voldemort definitely used Inferi the first time around. I think he used them extensively. I would think he probably had Giants helping him too. I agree with Eponine that Dementors probably didnít join him because otherwise the Ministry wouldnít work with them again.
I donít think he used Goblins. I donít think Goblins would ever submit to wizards which Voldemort requires, so I donít think Goblins would ever join him. They would probably remain loyal only to themselves. I donít think house-elves would join Voldemort unless their masters commanded them too. They donít have free will to choose to join Voldemort. I can see him using werewolves.
With other dark creatures and so on that Voldemort would have used, I think it's also important to consider the flip side of the coin. Okay, would Voldemort have used ghosts and goblins, etc, but also - would they have had a reason to join him?
Some dark creatures may not be a position to be motivated one way or another. I'm thinking of Inferi here (which Voldemort most definitely did have in the First War), which are creatures, but not thinking, breathing creatures that could either a) decide to join Voldemort, or b) be magically persuaded to join him. They are just things, to be controlled by magic. Other creatures, such as dementors, might arguably fall into this category, depending on whether or not you think them capable of thought or not.
I think Justice is right on about the goblins never submitting to Voldemort. They are clearly a fierce race with a lot of pride in themselves. They might have joined Voldemort if they saw that it served their interests, but I doubt that ultimately they would have believed joining him was beneficial (even if they did initially), given he was proposing wizard supremacy over all the world, not just the magical world.
The same goes for giants. In the books, we see how even Death Eaters had to negotiate with giants, rather than purely use magic to control them. But giants have had it pretty hard under wizards and so naturally might be more inclined to join with someone who gives them opportunities to attack humans at will. Werewolves are similar also, having had a pretty crummy time within wizarding society and thus being more likely (like Greyback) to want revenge. Vampires are another example of a possibly marginalized group that might be aching for revenge.
As for ghosts, I don't see Voldemort using them, at least not extensively. What motivation would ghosts have to help him? Unless they were strong believers in some cause or another in life, I doubt there is much that could persuade a ghost to help Voldemort or anyone else. True, they might be susceptible to some kind of magical control or another, but like things such as the basilisk attack, I imagine the success of this control would be hindered significantly more than if it were a real person.