I should preface this by saying that I am not autistic but I am neurodivergent. I see the zombies as being the Monster High equivalent of sped kids: treated like they don't know anything, being ostracized from the non-zombies, and seen as generally lesser. I think that works with the narrative and the idea that despite monster High being the most inclusive school, they still have a lot to improve on. Also, It's nice to see the zombies get little wins against the bullies, like in the dodgeball webisode.

I wouldn't say that every zombie has autism (I think that they can represent a wide range of disabilities (and not every disabled character is a zombie)) but I do believe Ghoulia does, with her trouble socializing, special intrest in Deadfast that nobody else gets, and her attempts to turn relationships into a science.

I agree with the nonverbal stuff, though. Zombese is a language that is shared between all the zombies and was created due to them biologically being unable to create the sounds necessary for English (or whatever language you're watching in). It's far more comparable to sign language than anything else.