I've spoken with a number of people who identify as HOH and feel the same way, too, that at work and at home they do just fine, but truly, the group they feel most 'at home' with consists of fellow HOH -- similar issues/interests, a common language and vocabulary, a physiological distinction from others. I had always thought of them as being somewhat culturally HOH, but I guess they might extend the definition and consider themselves an ethnic group, if they feel like one.
The very young adults and teenagers I've met who grew up with CIs and have met throughout the years at camps and events, have developed online relationships despite being dispersed far and wide, often talk of a strong kinship with other CI users. My daughter's closest friend is also another CI user at her school. Again, I tend to think of this as a cultural connection, but perhaps some day she will self-identify as ethnically CI Deaf as well as ethnically Chinese. Although hereabouts, I suspect there's more of a Red Sox influence than anything else in our culture
and she'll more likely consider herself a member of the Red Sox Nation.
Using "ethnic group" interchangeably with "cultural group" seems to dilute some of the meaningful distinctions between the two concepts, but I have no issue with what people choose to call themselves. As Flip has mentioned, though, I too object to strangers telling me they know better what ethnicity my child is and demanding that I change my child's behavior according to their definitions. I see her as ethnically Chinese, culturally American, and culturally Deaf)