He can.... The protection only wards of Voldemort himself, so any other person can kill Harry all the same. This is (although not mentioned in the movies) also something that happens when Harry willingly takes the full blast from Voldemort's killing curse during the Battle of Hogwarts. Although Harry survived.... again... Harry did out of love for his teachers, fellow students and other people at Hogwarts the ultimate act of sacrifice, causing the same protection over them, and Voldemort himself was unable to kill anybody for the remainder of the story, yet the Death Eaters and other followers of Voldemort did still kill...
In other words, if Hermione was able, to cast AVADA KEDAVRA on Harry, the curse would just have worked normally....
