No and yes. Southern Pacific natives are actually Australoid humans, different from the Negroid ones from Africa. The natives have extremely dark skins as Africans, true, but do not have African ancestry, nor are mixed as such. You can tell by their skulls, the differences are very obvious. You can find in some islands in Melanesia, dark skinned natives with natural blonde and red hairs too. They weren't "mixed" with Europeans, those are genes that only exist in that part of the world.
If you use "black" as = African ancestry, then Samoan people are not black in that sense, they are black because they have some of the darkest skin colours in the world, but their ancestry is 100% Oceanic.