Survival. Survival is the Talent used in skinning or cutting off parts from creatures (so essentially, get yourself a skinning knife if you want some hide).
So yes, you can use parts from monsters, but it is whether or not said parts would actually do anything is the real question (not every monster part does some strange thing with alchemy. Mystical creatures maybe, but no this isn't Skyrim where every piece of every creature has some god damn alchemical property). I mean, of course if the creature spits fire or has venom then you could find like a flame sac or a venom sac as well, but you would have to be somewhat skilled in Survival to remove such things without damaging them (or just get lucky and make a good roll, but still a decent Survival Score is needed
So yes, you can use parts from monsters, but it is whether or not said parts would actually do anything is the real question (not every monster part does some strange thing with alchemy. Mystical creatures maybe, but no this isn't Skyrim where every piece of every creature has some god damn alchemical property). I mean, of course if the creature spits fire or has venom then you could find like a flame sac or a venom sac as well, but you would have to be somewhat skilled in Survival to remove such things without damaging them (or just get lucky and make a good roll, but still a decent Survival Score is needed