Saskia/Saesenthessis isn't a Scoia'tael either. I would have thought that she would be a neutral card but she isn't. On the other hand: Eredim is (biologically) not a monster but an Aen Elle (an elf). However he still is a leader of the monster deck.
I prefer Scoia'tael to non_humans personally because it gives a purpose to the deck. Non human just refers to a type of people which is not what gwent is about. The game is a war between different factions and non human is not a faction. Dryads help Scoia'tael whenever they can so they are allies to them and many dwarves from Mahakam join the scoia'tael as well.
Eredin and the wild hunt travels through the spheres just like monsters came from them so that's why they are in this deck, the "aliens nobody likes" deck so to speak.
I mean, who cares It's about a basic classification. Every card should belong in one of these factions, but I don't have a problem with dryads in the Scoiatel Deck, same as I had no problem with the cards of the Wild Hunt being available in the Monster deck, in TW3....