Hey Matt, I don't see too many fish that will literally erdicate them from your aquarium. It's few and far bewteen when you see one rid you of the infestation, but if one or two are taken down by a 6line, that's 2 more you don't have to kill lol ;)

The slugs actually will acclimate pretty well, you just have to acclimate them slowly. The problem is that they get sucked into powerheads often and as you stated, will eventually die unless it can be passed on to another person with a planaria problem. I have seen these slugs offered as tank bred, but unfortunately I cannot remember where from :(

Good luck with the flatworm exit, I hear it works wonders. Just make sure your carbon is in full effect once you have medicated lolol :P