Oh I 100 percent think he is evil. Being rejected by Mystra to me means he is not neutral. To give my frame of reference: The goddess of magic protects a certain dracolich from adventurers because he is constantly making new magic. His goal is to make super dragons, but she does not care as long as he keeps making new magic. So the fact that she rejected Gale tells me, if Larian holds to lore, that he has shadow weave which is from Shar not Mystra.
