Yup, those are the Jefferies tube conduits.
This lines up with the director's plans that you see I posted earlier, the rest of the Defiant sets were struck in S7 leaving only the bridge and engineering for the final season (at least the final chapter segment), due to space being needed elsewhere. It's why you barely see defiant based eps by the end of the series.
which even then engineering was redressed as the basement of Mila for the last 2ish episodes.
It kind of bothered me that in the episode where they were in Sloan's mind they just used the defiant corridors, as if the defiant meant anything to Sloan...
I also think that they had the Klingon bridge and the Dominion meeting room on Cardassia left up permanently for the end of the series but that is more so a guess....