Sorry, not really along those lines.... but Did Seven come up with a pip of an insight even while she was reaching the nadir of her cognitive overload in the Voyager Conspiracy? The direct rejoinders to her blatherings about the tri-cobalt detonation at the array, danced around addressing the issue of Tuvok's delivery yield determination. Whether or not their use had been proscribed at the time of Voyager's mission (it seems unclear when the Second Accords went into effect, per a number of different sources), why would Voyager have had them in their inventory at all? Given the assignment, there would not appear to be any reasonable justification. I suppose if not yet banned, the weapon might simply have been a default bauble in the armory of this class that was a shiny additon to the Federation's stable. Thoughts?
The Dominion was a shadowy threat and who knew what the Maquis had up their sleeves at the time. In the Federation's defense, it's better to have something and not need it, then need something and not have it.
Perhaps Voyager was part of an experiment to see about including tricobalt devices as part of their standard complement. It could explain why the ship had so few torpedoes (before they got the torpedo genie that is), tricobalts could need special storage so the number of photons had to be reduced.
Tricobalts are just explosives like dynamite or c4. Most ships would probably have some, or could make some.
Interesting thoughts here on previous uses of the weapons and their status through ST:Insurrection. http://www.ditl.org/article-page.php?ArticleID=37&ListID=Articles