I have been using Lydia and have noticed the following: If I put on a ring, armor, boots, necklace and head piece all with bow damage percentage increase, my bow damage rating in my own inventory screen goes up to about 140 for an ebony bow. If i then give this bow to Lydia, the damage on the bow is the 140. If I give her the bow to start then give her the clothing with bow damage percentage increases, the bow damage remains at the base level in her inventory screen. Same thing if I give her the bow with bonus damage to start then give her the clothing. The bow damage always remains the same as what it was when I gave it to her...so do enchantments on armor and such actually provide a benefit or bonus to your companion? Perhaps it is just not visible? Thanks!
Enchanted gear does work on companions, but they don't take enchantments into account when choosing the items to equip. What you're seeing is the stats adjusted for your character, because the companion's inventory acts like a container.