Yeh you may find Saudi blacks called Al fullata. Which is a Arabian butchering of fulani. And yes a lot of these madow arabs are miskins of arab slave trades. Oromos were enslaved bya arabsFulanis/Hausa came to do Umrah/Hajj, I don't think they were enslaved because they still have their surnames.
Unfortunately, Oromos were enslaved and also other Madows who don't know their roots & had to adopt Arab clan surnames like Al-Dossari, Al-Qahtani etc.