Yes most unconscious people can hear you even though they cannot respond to you.
I have talked to an unconscious person before and they were able to move their eyelids a bit letting me know that they could hear me.
So yes for some people who are unconscious they can hear you but some may not be able to hear you.
Still even when someone is unconscious it's a good idea to talk to them to at least let them know you love them even if they may not be able to hear you.
Most unconscious people and even those dying people can hear you.
That is as long as they have their hearing still.