My Question is:- Is private messaging a player (Traitor/Detective buddy or even Innocent) something such as 'Plant C4 in House' or 'Check dB.420's Corpse' considered Ghosting if the Sender of PM is Dead?
Yes, tho it doesnt matter if you are alive or dead. The way the rules portray ghosting, if you use any form of 3rd party chat that is not TeamChat or the open chat ingame, to give any information that is related or can affect the round. It is considered Ghosting. Telling them to do something that the player may not have thought about doing, will influence the round.
Yes and yes. If you're providing them with information or knowledge of something they weren't thinking or aware of, it's ghosting.
Yes. Anything that can alter the game is considered ghosting, even something as simple as checking tab menu. Just don't message alive people about in-game play, even if it is false information. This applies if sender is dead or alive.