can your necromancers zombie(s) gain proficiency?

so heres the set up, Our Necromancer (Hes actually an abjuration wizard, but for the sake of this post we'll call him a necromancer since hes taking those spells) has a small hoard of undead. One of the items i awarded the players was a crown of intelligence. I thought "Well clearly they will give it to the big, dumb fighter, right?"

But our necromancer had other plans. He told one of his zombies to attune to it, so now "zog, the zombie general" has a 19 INT stat, and has become a proper character with his own personality. something akin to the knight of the necromancer.

He wants to flesh out Zog by allowing him to learn armor and weapon proficiencies to make him more effective, and i think its a good idea, ive even considering giving the zombie "Levels" (not actual class levels) to boost its HP but thats a whole different conversation.

My question is: Can NPC's gain proficiencies, or is that strictly intended to be a Player-only feature?