I don't have any medical proof to back this up, BUT given the considerable loudness of an AR pistol, I wonder if you'd only suffer a "little" hearing damage down the road, or if you'd suffer some serious and immediate hearing damage.
All I know is, with pistols, inside the house, during an adrenaline rush, for me personally, the sound is not loud at all, and more of an after-thought than a primary. My ears weren't even ringing afterward.
On the other hand, a 20" rifle firing the next bay over on an outside range under a metal cover while we were SUPPOSED to be on "range cold" (no plugs) hurt so bad I immediately and involuntarily jumped up started yelling a stream of cuss words at the guy before I ever realized what I was doing. If he had not been so submissive and apologetic, I'm sure I would have started punching on him just as involuntarily.
Afterward, I had a sharp pain in that ear for a couple of days, and I have definitely suffered immediate and noticeable hearing loss in that ear.
Anyway, I realize that being dead means 100% hearing loss in both ears anyway and I doubt a shotgun is going to be less damaging, so I'm not against the concept, but I think any steps you can take to protect your ears in advance would be worth the trouble. (suppressor, Pig, earpro, etc.)