Harla and Somali were occupational terms.
The entire Harla division was led by Sultan Mohamed (circled in blue) during the war. Sultan Mohamed happens to be a close relative of the imam. He was chief of one of the Harla tribes from Zerba. Today he would have been seen as a Somali but during Futuh he would have been seen as a Harla
Then the tribe of Zarba came up after them. Their chieftain was the sultan Muhammad, son of the paternal aunt of the imam. With him were one-thousand and-sixty notable infantry, and forty knights. The imam made them welcome and showed them his favour. He [sultan Muhammad] resided at Harar. The imam was exceedingly delighted at this and gave thanks to the Most High God.
His nephew Imam Mohamed Gasa bin Ibrahim bin Umar (circled in black) who was the governor of Bale at one point moved the capital from Harar to Awssa to start the Awssa Imamate. He appears on the list of rulers that ruled Harar which was compiled by Ahmed Sami in his Jadwal. 53 to 58 were all Gasa’s bloodline.
Lineage tree of Imam Ahmed, His cousin Sultan Mohamed that led the Harla contingent and Imam Mohamed bin Ibrahim bin Umar that moved the capital to Awssa with bunch of Harla’s accompanying him.