In the episode One Little Ship, a Jem''Hadar attack ship confronts the Defiant while the latter is in the middle of an experiment. The Vorta on board is Gelnon. The ship departs after depositing a number of Jem'Hadar on the Defiant.
In the next episode, Honor Among Thieves, Gelnon meets with several members of the Orion Syndicate, including Miles O'Brien, on Farius Prime.
It has been shown that Dominion intelligence is VERY good. One of the Weyoun clones stated that Sisko's psychographic profile was required reading for Vorta field supervisors, going so far as to claim he knew more about the Captain than Sisko did himself. Every Changeling infiltrator seen was able to convinvingly impersonate high profile figures in the Alpha Quadrant.
While it wouldn't be surprising for a Vorta to lack an encyclopedic knowledge of every Starfleet officer and crewmember in existence, it seems odd that a Vorta field supervisor operating in the Alpha Quadrant wouldn't be familiar with at least the senior staff of DS9 (and the Defiant) especially considering a recent encounter with said crew. So why did Gelnon not recognize O'Brien on Farius Prime?