Well, responding to joe's question from discord here, whether I consider this an exploit.
Exploits in general are not listed in the OP, except the newest hotseats, which however doesnt mean they are allowed. It always depends on admin, I personally am more strict on exploits ...
Anyway, few turns ago it was allowed to move an allied bribed sharnhelm general if Im not mistaken (and maybe allowed due to not having 4 units in fort anyway from a part? Cant really remember details and it wasnt discussed on the thread it seems). However, I think this is another level of this issue, as those allied bribed units (that were put next to the fort on Sharn's turn, so they would be bribed more easily) were not just used to make a hole in fort wall, but to win a battle, Ventos would otherwise not win (correct me if Im wrong). And this is not just a battle, but probably might be the one that decides who wins this round it seems.
EDIT
So yea, I consider this an exploit...