Nah, Sisko gassed a whole planet. He should've been clapped in irons for that one. It's like a us officer gassing an Arabian village because he thinks there's a terrorist cell there.
Then again Sisko was never preachy about upholding humanity's principles in the same freaking episode he was going after his nemesis with a vendetta. Would Janeway have killed him? She was willing to kill that blueshirt if he didn't sell out his captain, so yes I thinks she would've. One of the few times Chakotay stands up to Janeway, but he picked a good time at least.