Could someone in a coma hear?

No: if they can hear, it is not a coma. Of course, there is that whole out of body argument. Cannot comment on this. No matter what any Physician tells you, we are not smart enough to know whether or not that is true yet.

Depends on level: Coma is a complex condition and there are various levels of coma. In deep coma one can not hear but it is not like the movies where someone in a deep coma suddenly wakes up. People emerge gradually into lighter stages and as one emerges into the less deep levels of coma they are able to hear. See http://calder.med.miami.edu/pointis/tbifam/coma1.html