In DS9 episode "Tears of the Prophets" (S06:E26), Sisko is holding a conference where he attempts to convince the Romulans to help invade Cardassia. In the background is a guy in a TNG-style Starfleet uniform with no pips on his collar. This presumably makes him a crewman, although there may be pips that aren't visible. Of greater interest, however, is that he's wearing an old uniform that had been phased out by this time. The TNG-style uniform had been out of use for at least two years at this point in the Dominion War, possibly even longer.
Who is this character and why is he wearing the old-style uniform?