Can my follower hold the same legendary item as my character?
Yes you can. I just tested this by buying and equipping 2 cheap uniques. Even though I could not equip both on my character, I was able to equip one and give the other to my follower.
I also tried to give my follower 2 of the same unique ring. He was only able to equip one of them, so followers also cannot bypass the unique equipped requirement.