Yes, a dead person obviously doesn't need medical attention. The medical examiner is called.
The codes aren't used for the listener to know what it is going on. It's used so the ambulance personel know what is going on and know what they need.
For example, the wreck on 220 had services calling into the ambulances and saying they had one priority one and two priority fours. They only needed services for one patient then. In reality what they had was one patient in need of series care (priority one), another "victim" who refused treatment and walked away not wanting to be looked at (priority four) , and another "victim" who was obviously deceased (priority four).
one priority one
two priority fours