This page specifically references Torias as being in Starfleet:
...But it appears to be in error. Nothing in the episodes suggests the shuttle crash was related to Starfleet, and Torias went to a Trill hospital afterwards. Or more exactly, the Trills were able to pretend that Torias had gone to such a hospital, while in fact he died and Joran got Dax. Had Starfleet been involved, especially as the employer of Torias, the odds of this happening would have been low indeed.
Being spotted would mean standing out amidst Kirk's crew. But being spotted doesn't mean you would be immediately recognized as Trill. We have seen at least two spotted species, the Kriosians ("The Perfect Mate" and "Precious Cargo") and the DS9 era Trill hosts. Or perhaps those are one and the same species..?