Yes they were most definitely agricultural Somali. We must do some archeology for turn if the millenia till the oromo and ethio semite migrations into the hararghe region displacing ethnic Somali to find out who the harla were.I claim to be no linguist, but Somal, Tomal, and Bimaal were most likely occupations or easy ways to distinguish ourselves, the harla were farmers and most likely the name given to them was from the outsider, Arabic in origin, Biimaal probably being the original name, I'm not saying modern day Biimaal are Harla.
CookedA submission from the United Kingdom says the name Harla means "From the field" and is of English origin