And as a follow-up, how have they survived for so long? Do they usually regard themselves as Arabs or a different ethnic group, and how have they been treated historically by their Arab masters?
I imagine you are referring to Mehri, Hobyot, and Soqotri? These are South Arabian languages that survived near Yemen and Oman due mainly to their geographic isolation from the rest of the peninsula. Southern Arabia is very mountainous, and the Soqotri speakers from Socotra are isolated in their island. By virtue of shared faith and geographic location, the Al-Mahra people and related groups largely consider themselves Arab, though tensions between these minority groups and larger governments has occurred, as evidenced by the Dhofar rebellion, wear local speakers of South Arabian Languages took up arms against their government.
The people of the fifa mountains in Saudi Arabia have their own language, they speak Arabic as a second native language and consider themselves Arabs.