I was just re-watching this episode with my wife. It's the episode where Seven fights The Rock "America's Smackdown Hero takes on Voyager's Battlestar Babe", but more importantly it features two DS9 supporting cast regulars Jeffrey Combs and J.G. Hertzler. At the very end of the episode, after Tuvok and Seven finish reflecting on their experiences, they insert just a short segment of the DS9 theme into the music before the closing theme. YOu can hear the cue right around 1:35 here:
I'll admit, it's a bit DS9-esque (I know nothing about music, so I can't describe it any better than that) but it is certainly *not* any part of the DS9 theme.
Both cues are by Dennis McCarthy, so no surprise there. Probably also why the first two notes sound like Generations. (And speaking of Generations, McCarthy swipes from himself pretty heavily during the Romulan/Cardassian vs Dominion fight in The Die is Cast.)
If you want to hear the DS9 theme music -- at least a woodwind variant of it -- watch the DS9 episode "Sanctuary". It was a musical performance at Quark's by a Bajoran musician (played by William Schallert). I guess you can say it was a DS9 tribute to itself.
Actors move around from show to show a lot. The actor who portrayed Dr. Mora showed up in TNG and Voyager. I think they tend to stick with people they know can handle the alien makeup and long days.