It’s the intention you have that counts and the only judge of that will be staff and it doesn’t matter what excuse you got. It doesn’t even matter what location you are ghosting, as long as a staff thinks you are doing something to gain unfair advantages towards other players.
Punishment will be for everyone involved. No staff will not need any proof for punishing you.
To answer your question:
“A thief is hiding outside of a dungeon, and two others in his party are hidden and waiting inside. All three characters are being controlled by different individual people. Someone recalls in, the thief informs the other two, they PK the person who recalled in at ease with the preemptive knowledge, loot, and leave.”
This is considered camping and not ghosting, the intention is to wait for players to kill. Would it have been a thief standing outside a dungeon with the sole purpose of calling on his friends to kill it would be considered ghosting.
Since ghosting isn’t something you can define by an action since it’s the intention that counts, staff will decide if your intentions are pure or not. Any tries to bullshit your way out of it will only result in longer punishments.