First of all, I am unsure if this is intended or not. The minecraft wiki does not tell us.

As of 1.8 14w06a, giants now show the armor they wear, except this does not apply to playerheads, even though giants have the same layout as zombies (apart from the size and AI).

As a server owner I tried equiping a giant with a custom-textured playerhead to make it look like a giant floating eye. To my surprise I noticed giants only render "vanilla" armor and no items such as playerheads while worn. Especially for game developers out there who work with custom mobs, it would be amazing to see giants support this item.