I'm wildly speculating here, but there seems to be some fundamental incompatibility between Betazoid telepathy and Vulcan telepathy. (See the Voyager episode Meld
.) Everyone thought Tarses was part Vulcan, not part Romulan, so perhaps Satie's assistant didn't want to do a more detailed scan because it would have been risky.
The alternate explanation is that it would have made the episode a lot less interesting.