Original dervish is right there are Somali clans assimilated by Amhara and oromo, and there are Oromos and Amhara assimilated in Somalis, all in all the Horn of Africa is one family after all. Ethiopia is national identity its not an ethnic group per say.
nah somalis didnt absorb because of geographical and religious barriers, it gets blurry depending on how far back you go, but the xabasis have recent genetic input (dating back several thousand years) which today caused them to form a distinct population and somalis form a genetic a homogenous population indicating a lack of outside admixture. If we had oromo or amhara admixture wed have higher omotic and euroasian respectively, but we dont.
Oromos are the ones who have absorbed countless muslim (gurage, Somali) and xabasis during their massive expansion after the exhausting Adal and Solomonic war.