Originally Posted by
Comun
Completely different occupation. Onmyouji is a member of the Bureau of Onmyou, an actual government body of the Heian administration, where the members were dedicated to use their mystical knowledge of laws of the universe in service of the Emperor, the governors, and the nobility. Abe no Seimei was an onmyouji. Ashiya Douman and Kiichi Hougen were not.
Onmyou priests, onmyou monks, or however you want to call them, were more like folk healers. People with knowledge of onmyoudou but completely unrelated to the government, and 99% of the time, distant from the capital. They were cases like Kiichi Hougen, who was a stationary hermit in Mt. Kurama attending the needs of whoever climbed his mountain to ask; or Ashiya Douman, a wandering monk from Harima who travelled the faraway southern lands the Heian administration couldn't give less of a shit about, helping every person in need he would find along his way.