The cloaking devices used by the people in Nightingale were so uncomplicated that Harry and Seven were able to fix, upgrade and rewire that first-generation-cloak on the fly without knowing anything about... Basically it was like an episode of MacGyver if consider how easily they mastered the technology without being familiar with those systems if it was only a rubber band engine being fixed.
Just that Harry knew anything about this FORBIDDEN technology means that it was probably on par with the Cloak which Kirk stole form the Romulans a hundred years earlier or even more basic than that!
Janeway used a form of cloaking technology in Dark Frontier to stay invisible to the Borg, that might count? But it wasn't clear if that tech would work against any one other than the Borg except that it masked them from the Borg scanning technology as much as their physical senses.
If she's going to use a cloak, then she might as well use biogenic weapons too. Law shmaw. Although if it's the spirit of those weapons bans is about killing populations too efficiently or quickly or even slowly or halfassedly, if you're not going for a humane megadeath then you're a right bastard, then her nanotech weapons to kill Borg might have to be shelfed as well and be labeled as a little monstrous for abiding in the creation of.
The Voth had cloaks. The devour had cloaks, and Voyager mastered that technology totally. The scientific method people had cloaks. That hologram who fell in love with Tuvok had a cloak. Hell those Klingons with the plague must have had a cloak even with out Enterprise pushing the inventin of the cloak backwards...
Besides, Janeway thought Ransom was a bitch for always finding stellar anomalies to hide in... Now that bugger, he should have built a cloak, because it was in his character!