Weren’t the Somalis and assigned their own leases and put into different battalions and they kept falling out during the war? I don’t think we can categorically state the Harla were a Somali clan.
The Somali clan of Zarba led by Imam Ahmed’s nephew rose from the country of Harla during the mobilisation of Adal’s army. There is no modern ethnicity with a direct contemporary 16th century link with the Harla, only the Somali people.
Harla was either a life-style occupation like the Tumal or it was a specific geographic region. In both cases the evidence leans to them being what would today be considered a ‘Somali’ group.