There's three kinds of Oromo:
- The Habeshi ones who are genetically, linguistically, and culturally indistinguishable from the amxaaro. The live in the more central/Northern parts and are called, I think, Arsi, Shewa, Bale or something. The live in places like Addis Ababa all the way to the Bale mountains.
- The Eastern Oromo, the true Oromos. They are usually called Afran Qollo (Afar Qollo in Somali) and live in the eastern portion with the Somalis in Galbeed. They've managed to absorb and assimilate a few Somali clans like Gurgura, Jaarso, Gaadsan, Garre etc. This group would be closest to Somalis genetically and culturally, though they are still quite different to us.
- Southern Oromos. This group includes Borana who live in the southern parts of Ethiopia and Northern Kenya. This group has a lot of nilotic ancestry and admixture.
That's my limited knowledge on ethnic groups in the horn.