And had Spock simply mind-probed the captured Tomalek,wouldn't that have spared a lot of to-ing and fro-ing?
(And please,don't give me any guff about Spock being reluctant to use his gifts that way...ST6 puts the lie to that).
James Swallow's 2011 novel Cast No Shadow
covers the question of what Spock did to Valeris in Star Trek VI
. Suffice it to say that it's not something he'd do again.
Also, your question could just as easily be asked of any telepathic individual in the Federation. That the Federation Security Agency did not simply have another Vulcan, or a Betazoid, or an Ullian, or any other telepathic Federate, probe Tomalak's mind, strongly implies that such things are by the 24th Century considered a violation of Federation law.
It's interesting; J.M. Dillard's novelization of STVI plays that scene a bit differently, though not really in a way that reasonably consistent with the film. Spock is depicted as being much less forceful, and still getting what is needed. There is no indication, so far as I recall, that Spock was doing anything questionable, the way Dillard depicted it.
That novelization was an interesting ride...
Back on topic, though, it is a little
surprising to me that Starfleet was not shown vetting, at least implicitly, the Romulans, with or without the use of telepaths. (Maybe I'm forgetting something?) Troi was shown doing that all the time, in a way that didn't seem to be perceived as any more privacy-violating than observing someone's body language.