"Pope Leo III was canonized by the Catholic Church in 1673, his feast day being June 12. He is not listed on June 12 on the Western Orthodox calendar that I have. Perhaps this is because he was canonized after the schism, even though he lived before the schism."
He seems like he should be sort of a bugaboo for the West, considering his fiercely strong stance towards protecting the Symbol of the Faith. For a good study of his role in the Carolingan controversy, read "Franks, Romans, Feudalism, and Doctrine" by Romanides or "God, History, and Dialectic" by Farrell. I believe that most Easterns would find him a champion for the Orthodox Faith.