No, it's absolutely true and found even in colonial documents:
RICHARD PANKHURST, The Trade of the Gulf of Aden Ports of Africa in the Nineteeth and Early Twentieth Centuries, Journal of Ethiopian Studies, Vol. 3, No. 1 (JANUARY 1965), pp. 36-81
www.jstor.org
Edward A. Alpers, THE SOMALI COMMUNITY AT ADEN IN THE NINETEENTH CENTURY, Northeast African Studies, Vol. 8, No. 2/3 (1986), pp. 143-168
www.jstor.org
Abdi Samatar, Merchant Capital, International Livestock Trade and Pastoral Development in Somalia, Canadian Journal of African Studies / Revue Canadienne des Ćtudes Africaines, Vol. 21, No. 3 (1987), pp. 355-374
www.jstor.org
Livestock from Northwest and Northeast Somalia was so important to the survival of Yemeni ports like Aden that the gaalo plainly stated they'd be finished without Somali exports or if Somali workers and traders, who were everywhere in towns like Aden and Mocha, performed a mass exodus which they indeed threatened at one point when the Brits were about to enact a plan to deport 2,000 Somalis only to pull back on the plan for fear of Aden going under without the Somalis.
The livestock exports from the northeast in particular were so extensive during the mid to late 1800s that it effected clan migrations. As in, MJs began having to migrate more southwards, both overland and via ships, due to the sheer change in dynamics from the massively increased herds and overused land in their native northeast areas.