Could someone tell me what reverberation sounds like coming through a hearing aid.

If you are talking about typical room reverberation it sounds with or without aids like an echo. If you are referring to hearing aid internally generated reverb it could sound like an echo depending on the delay time and other factors… Quite unusual to have an aid produce loud delayed sound.

One of the things that pathology of the human hearing system damages is the ability of the brain to filter out the echo’s. Normally hearing persons are not even aware that every room has some reverberation (except an anechoic chamber). Ed