I did the research exclusively for TibiaQA.
For that purpose I travelled 400 times from Venore to Darashia.
I was sent to ghostship at tries number: 22, 36, 72, 110, 139, 188, 217, 235, 278, 309, 355, 394.
It means that I was teleported to Ghostship for total amount of 12.
Doing quick maths, we receive the result 12 / 400 = 0,03
Answering the question, the possibility of being sent to Ghostship is around ~3%