Nope. All six of the main books are six separate crews dealing with six separate parts of the big overarching story. Apart from the big mass holodeck scene, they barely cross over at all. If you're only following the DS9 stories, the TNG entry is not vital. Yes, it's the one that most directly addresses the actual problem facing the galaxy, but that's not really the most interesting part of the whole thing anyway. All you need to know from the TNG book is basically - "Don't worry, Picard's on it."
As for book seven, well that's different. It's a short story collection that brings together the codas from the six main books. The DS9 portion of that is fairly necessary, but I suppose if you really really had to, you could skip it, at least plot-wise, espcially if you don't give a toss about the other five. Character-wise though, it's very much worth it.