Can Aniimo creatures wear skins?

That splits the cosmetic layer in two. Character skins cover how you look, creature skins cover how your Aniimo looks, and both sit in the same category of cosmetic items rather than being separate systems.

Irisalis shows what this means in practice. Its appearance customization system gives you cosmetic skins, not separate evolutionary forms. The look changes and the creature underneath stays the same one. If you were expecting an alternate appearance to signal a different stat line or a branching evolution path, that is not what these are.

It also helps to know where the creature itself comes from. Aniimo are not handed out through gacha character banners or pack pulls, and no real money buys one. Every creature in the game can be encountered and captured in the wild through open-world exploration, which means deploying Anipods, setting traps, sneaking up on things and using the terrain against them. The creature is the part you earn by playing. The skin is a layer you put on one you already caught.

Not settled: How creature skins are acquired, and whether a skin attaches to the single creature you caught or to every one of that species you own, is not settled yet.