Just a thought here. Is there anything specifically making you sure it was humans that took the ducks and not a predator? I ask for a couple of reasons. First, If a person wanted to steal the birds I would think that they would take them quite a distance away. Far enough that you would not hear them and potentially find them. If that was the case, the birds, especially with mangled wings, would not be able to make it back to your property. Secondly, while I do understand about red-neck mentality and the lack of logic, it does not make sense that they would mutilate the wings instead of just outright killing them for food or other purpose. If they were just wanting them to stay put and were trying to "clip" the wings, it takes me back to my first point. Why would they steal the birds and keep them close enough to you that they could walk back home? And, why take some but release the others?
I'm sure that this is tremendously traumatic for you and the birds, but to me, it sounds like a very typical predator (i.e. coyote pack) attack. The missing birds are either dead or scattered quite far away. Those that were wounded, but managed to escape, made their way back home. When birds are trying to fly away from a predator the wings are one of the easiest parts to grab and can sustain the most damage. I had a similar situation last year when something got to my birds when they had not been put up by dark. Most of the flock was dead in the yard, but several were missing, some were wounded terribly and had to be killed. Out of all the missing ones, a couple returned the next day. Chickens are not as good of flyers as mucoveys so wound up being killed while still in the yard. That same summer a friend had a predator attack in her yard while she was at work. Her neighbors heard all of her ducks scatter but did not see what it was. Most came back but the muscoveys never returned.
I understand that you have 9 dogs and that makes me think coyote even more. Most people, redneck included, would be afraid to enter property guarded by dogs. While dogs can be a deterrent to predators, coyotes are especially vigilant and will watch and wait until the opportune moment to strike. They would be more likely to risk an attempt on the birds than humans would be.
I'm not ruling out the possibility of humans being involved but know how easy it is to get upset and find it difficult to look at things objectively in that kind of situation. Whatever it was, I wish you well and hope there is no repeat. Unfortunately, if it was a predator, they will be back soon since they know a meal is at hand.
Richard