Hi
And one would have to define what Arab is supposed to designate precisely for this period. Is it the Yemenite or Hedjaz kingdoms ? Already some differences between desert dwellers and coastal residents, Jews, Christians or Pagans.
Then the fringes of Iran ( south coast) the Sinai, Syria ... the Ghassanids and Lakhmids and others. The Saraceni most feared by the Eastern Romans, and probably those who really did the early islamic conquest ( as Mekka may not have existed yet at the time). You have Iranian Asavaran influence, Aethiopian influence ( they conquered south Arabia), Roman influence, up to some point for each flavour. That makes for a large range indeed, but usable in multiple armies.