Why was Alexander The Great able to have a prophecy, of seeing the Kohen Gadol, before he had victory at every battle
It was an apparition, not a prophecy. A prophecy is a message from God. Being that he was entitled -for some reason- to conquer the known world, things went his way. The Gemara mentions how Nevuchadnezzar had signs of success. Josephus records apparitions the Hasmonian kings had before a success.
In fact, Michael Greenspan has in his documentary, Against All Odds Israel Survives, how some Arabs saw an apparition which scared them off.