sextus the crazy said:
I think the only group with less representation would be the blacks. Seriously, outside of derrick green of Sepultura and Abasi Tosin from Animals as leaders, I cannot think of anyone.
Canadian black metal band, Blasphemy, has a black guitarist (Caller of the Storms).
UK thrash metal band, Evile, had a black bassist, Mike Alexander, though he sadly passed away.
Suicidal Tendencies has a couple of black members, though I'm not as familiar with the band to know their names or chosen instruments.
For a more obvious example, brutal death metal pioneers, Suffocation, has for a long time had two black members. Terrance Hobbs on guitar, and Mike Smith on drums (though the latter has left the band twice).
That's about all that comes to mind though. You're right that it's another very small minority in metal, at least in the public eye.