It would almost certainly be a community with very few if not zero active posters, and there's already a few relevant communities on .world, and nothing's stopping people from posting d/Deaf or HoH-related content on other communities... But even keeping all that in mind, I still think having a /c/deaf would be nice anyways.
The community could also be called /c/dhoh or something else entirely, it depends on what people prefer.
c/canyouhearit?