I've seen people successfully fistweave twins (dependent on strategy). Otherwise, bracken you want to sotws for spamming mushrooms, and tectus you need to focus on tanks in the last phase, although I see fistweaving probably viable for farming tectus. Koragh you may be able to fistweave for a little, but certainly not the whole fight.
I haven't done imp, but from what I've seen you can fistweave parts but the healing gets so intensive you're better off with your healing talents anyway.
you can use whatever the heck you want to on kargath...it's kargath..