I searched and didn't find that this question had been asked before. Pardon me if I'm being redundant... I noticed that the Terok Nor trilogy's logo matches the Deep Space Nine relaunch logo, not the logo for the television series. There have been DS9 books since the relaunch have had the older logo -- such as Hollow Men, and the Prophecy and Change anthology -- so I wonder: Does the logo indicate that the Terok Nor trilogy is part of the relaunch? Obviously, it's set before "Emissary" rather than after "What You Leave Behind", but I'm thinking that maybe the logo is a subtle hint that the seeds of future relaunch storylines are being sown in these stories. I'm getting a real kick out of the books so far, but I would love to see if Marco or the writers are willing to share anything about the logo choice.
Not "part of," per se, and "Relaunch" isn't an official category anyway. But the Terok Nor trilogy is from the same editor as the post-finale DS9 novels and is in the same continuity. It builds on ideas established in previous DS9 fiction (including A Stitch in Time, which was published pre-"Relaunch" but is treated as part of its continuity), and future DS9 fiction will no doubt be influenced by ideas from it.