In Tolkien's lore every cardinal direction has a kind of morality associated with it. The west is always been a symbol for good, because that's the direction in which aman (heaven) is located. Every other direction is basically evil in some way, and among those the east is probably the most evil. So yeah there are some instances in letters and drafts where Tolkien refers to orcs as "mongol-like" because the Mongols irl were always "the menace of the east" to Europe. At least that's my theory about why he said that.
Black people do exist in Arda (the world), and those are the haradrim. We know they are directly analogous to real life africans because the land they live in is basically fantasy africa. In Tolkien's world Arda, middle earth is Europe, Rhun is Asia and Harad is Africa, in some old writings (when Tolkien was still trying to write fan fiction for bongland) they are even meant to be an alternate past version of earth.
If you want me to exposit on my idea of what orcs are supposed to be then do so at your own peril.