I'm not exactly sure what you're saying. How, exactly, does it "play no role in the novel"? Ezri and Julian are two characters with whom the readers are invested. We care about what happens to them. We see a reconciliation between the two of them that has been a long time coming. How exactly is that not playing a "role in the novel"? It's a part of the on-going story of all of these characters! I guess I'm just having a hard time figuring out what parts of the novel you think "play no role," and what exactly your criteria are for inclusion in the "role-playing" parts of the novel.
You say that the things the novel talks about have "no bearing on the events of this novel." I see it differently. I see these happenings AS the events of this novel. I think it can't be studied in isolation. This novel is a part of the on-going story of Deep Space Nine and its characters.