It does make a certain amount of sense - having the Emperor deposed and cut-off remnants of the KNF feeling betrayed. This is particularly true if the former Emperor has played on their feelings of betrayal in order to gain their support.
I would think though, that loyalists among the Hogosha might also have joined them - particularly anyone that happened to be pirating out in Dublin at the time...
What is less clear though - is how the Bretonians would feel about having the Emperor - the man who waged war against them - now on their side. I guess demonstrates just how desperate Bretonia has truly become!