The SimGurus said that Disabilities will be an opt-in feature anyway. So there won't be any disabled people in the game unless we make them.
Being unable to create disabled supernaturals would mean the devs knowingly limit our storytelling potential.
If we want to imagine that a Transformation into a vampire instantly cures any disabilities, no matter what they are or what their cause is, injury or chromosome error, insufficient vitamins, poison or a virus, becoming a Vampire cures it, then we just don't create vampires in wheelchairs.
I see the Sims as a game where we are able to tell our stories. It is literally the only game I know of where you can play as a fat, black, trans vampire (born female, partially changes into a man) who falls in love with a married woman.
If I wanted it (her is wrong because it identifies as male and has a partially male appearance, him is wrong because it is still biologically female and still has some female features, and since it's also a Vampire, I use it) to sit in a wheelchair as well, why would the Devs want to stop me or force me to sacrifice the Vampire part? It would limit storytelling, no matter what any vampire lore says.
If it can be accepted that vampires sparkle in the sunlight, vampires in wheelchairs can be acceptable as well.