Slugs do exude a very sticky white slime when threatened. I do not think the slime is harmful to your animals, but watch the newts to make sure they can open their mouths. You may want to try and wipe the slime off if it wouldn't stress them out too much being handled like that. I used to feed my tiger sal slugs frequently but she started refusing them (I think she hated the slime, and I can't say I blame her!)
Heather