No, they are casting material
I guess it would be a combination of both. The cases where, the dead victim is shown in the crime scene or in autopsy (not dissected of course), the real/live actors are made to lie down with real good make up to show as if they are dead bodies. However, for scenes where ducky explains the cause of death or anything else with the body dissected and laid down on the table, it is a fake corpse. Or, they will show a fake corpse whose body is cut up and then show only the face of the real actor in close-up to give you an impression that, it is the actors body that is cut up.
Poltergeist
Yes, NCIS is real.
Yes the NCIS building is real. It is located at the Washington, DC Navy Yard.
no
Yes, NCIS is a real organisation besides a TV show
Yes, there is an NCIS, the Naval Criminal Investigative Service. But no, the real NCIS is nothing at all like the TV version.
The Real NCIS - 2009 Hartley was released on: USA: 22 August 2011
Yes the show is based on the Real federal agency
Yes. In the 1982 film Poltergeist, in the scene where the mother falls into the pool and the skeletons attack her, the skeletons used were real, and were buried in the spot of the set. Likewise, in the 1987 Hong Kong film Men Behind the Sun, a genuine child's body was used for an autopsy scene. In the 2006 film Unrest, real bodies were used as cadavers.
The NCIS building is located on Sicard St in Washington, DC, in the Navy Yard