Fire healing, as mentioned before, depends on how conceptual and spiritual you are taking the idea of bending. In the end, honestly, it all depends on what the author decision. It might even be possible, but Azula/Fishie be completely unable to do it, at least not without being trained by someone who already knows it well.
Of course, that isn't any reason not to experiment. Ethical concerns are, but then, it's Azula and it's for a good cause, so... BRING THE TURTLEDUCKS!
Or prisoners, but that's a bit distasteful to start with and breeds far too much hate unless going after the scum of the scum like rapists and such, and those are not quite
that common*.
* And speaking of using prisoners, in another interesting factoid, the Fire Nation is likely to have far more cultural, social and legal hangups of doing so than the Earth Kingdom, although it's not certain. There's some evidence that they do not only take prisoners, but treat them better than you'd expect for the time period they are supposed to be in and how long the war they have been. Captured non-benders seem to actually be sent to prisons, not merely killed out of hand, and their prisons, from what we've seen, are better than you'd expect, even against foreigners who they have been at war for a hundred years.
Benders have it worse, mind you, but even so, most of the mistreatment seems to be mostly focused on removing their benders as a major threat, and let's be honest here, there's little way to do so without it either being cruel, prohibitively expensive or both. Take that platform they took Haru for example. The worst systematic case (that is, not a particular singled out individual, like they did with Bumi), would be the water benders, but then, really, there's little way of making sure they don't have water to bend and are able to do so at the same time. I suppose they could keep just about every bender drugged unconscious, but that's ridiculously expensive and ridiculously dangerous, specially if it had to be standardized and without far too many physicians to keep track of the prisoners.
And even all that? They are still taking a risk, with how broken master benders can be. See Bumi, or even Hama, even if she's not quite a
master at it for example. In all, for what the standards of the world seem to be, they seem to be pretty humane in their treatment of prisoners. The air nomads might have been better, but I have a feeling that their major punishment for those who wouldn't be willing to follow their social contract would be banishment or something like that.
