Zexion has mimic'd a person's weapon before, though that was Riku's keyblade. However, Zexion seems to prefer mostly ranged abilities for the most part, which largely means magic. Link is likely a far better swordsman than he is, so he would likely only go toward sword mimicry if for some reason he was forced to close distance and couldn't use magic. He might attempt to mimic the fire bit though, if only as a determent against anyone deciding to melee him.

Awesome on the latter bit, Zexion likely would seem to be rather decent/harmless upon first glance (sort of like Demyx lol) , its his mind, schemes and magic which is the dangerous part of him. (Though I imagine getting hit with that book of his could give quite the nasty headache, if thrown upside someone's head)