I personally wouldn't worry about the legal implications, but then again I'd be prepared to have experts provide information about why a trained homeowner should have such hearing protection available.
I'd expect said experts to point out that many SWAT teams use such equipment, for scenarios when gunfire is considered a distinct possibility.
I'd expect said experts to point out the likelihood of hearing loss from unexpected exposure to gunfire.
My military and aviation backgrounds would help, as it would be easy to document that I've had training with regard to hearing protection and loud noises (from the military side, specifically including gunfire).
And I wouldn't worry about it, per se, because if there's any question about an SD scenario, I'd already expect to need those experts, anyway.