Heresies and sects in your world

Basically the title, but also, a question: can a heresy exist if the religion has no canon or other official doctrine?

In my rpg setting, most dark elves's are monotheistcs, but a dualistic approach with xamanic influences is becoming popular due to the large-scale migrations. Also, the monotheistics are divided in branches which mirrors tribal differences. For example, the Jere tribe, which has a very strong hierachy, has a Patriach similar to a real-world Pope, while the scattered Auri tribe's priests organize themselves in cells which join in conclaves every year.