[You are absolutely correct that he would not heed a single warning about where to nap, and would do as he wished regardless. Emet-Selch is not a man to fear much of anything, let alone cutesy monsters of questionable design. While he's well aware of his unfortunately and unmistakable mortal state, that didn't mean much for him in terms of caring about being particularly safe...

Look, the dude has issues.

However, none of these issues help with him being endeared by his small assailant, though he does pointedly try to ignore her at first. A slight twitch to his upper lip being the main indicator that he's aware of the visitor. Granted, he's still not quite used to the weakness this body has when it's not being powered by his aether, so the weight of the small thing bouncing on his head like her own personal trampoline isn't something he can so easily ignore.

So, his face reflexively curls with disgust as he opens his eyes to look up at Maribelle. Wordlessly he reaches a hand up in an attempt to snatch the small Pokémon off of his head. No restraint nor attempted gentleness from him.]

Well, now... What have we here, hm? One of those malformed beasts—though, I cannot say I have seen one like you before.