In chapter 127 the people living on the Isle of Doom are described as having a “fierce loyalty”. Only, outside of swearing loyalty to Tommus and accepting him readily we don’t experience this.
This is especially important because of Talarius.
One aspect of fierce loyalty is closing ranks and an shared dislike for enemies. The D’Orcs from the Abyss hate Tiernon, and more specifically Sentir Fallon. The Tiernon troops on Nysegard really dislike Sentir Fallon. The folks on the Isle of Doom? Nothing.
Now, the amity between the forces of Light on Nysegard means that the Nysegard Doompire subjects are okay with Tiernon. They should still have a strong hate (even stronger than the Citadel of Light) for Sentir Fallon.
Not sure how you would work into the story — maybe during the discussion of how they allied with the Los Alvar and Shield of Tiernon?. But, I feel that this betrayal by an upper management figure in Tierhallon should have led to strained relationships. They couldn’t have forgiven so quickly.