Hard to say. Salt draws water out. It works on slugs because they're so small and thin-skinned they dry easily. These things... they probably do have permeable skin, that's why it's got all the mucus, but there's more muscle and firm tissue underneath.

[she tilts her head towards a gout of flame close enough to make skin feel tight and uncomfortable.]

Wonder what they think of fire. I haven't seen any over here but, there's less for them to eat, too.