Although, in a normal Mafia game the dead players get to see what happens at night. In this, they don't really have any more information than the rest.
That is only if you play it in real life, but I think Timballisto was referring to online renditions of the game as well.
The problem is, the dead are confirmed innocent and so whatever they say will be totally believable. That ruins one of the key points of the game (deciding on who to trust with their words).
