When I lived in Buffalo, Somalis and black Americans didn't rock with each other. They were segregated on opposite sides of the city and had very little interaction. The Somalis were refugees, dirt poor, FOB's, first generation, followers of Islam, different customs, different odor, language barriers it's easy to see why they stick to their own. The children typically went to different schools but I had heard there was a bit of ethnic friction in the larger high schools between the boys.
I don't see what the anecdotal evidence would do for you though. The census did allow people to pick their nationality and ethnicity after the race category and that detailed breakdown will likely be released too. The census doesn't give a fukk about what you talking about they don't care if shyt is kumbaya between ethnicities they just count folks racially. It's like an Irish cac that lives in Howard Beach, Queens saying he don't rock with Italians like that. At the end of the day still white and that's what the Census is looking to count.
Seattle is not a very black city at all even with East Africans included if you feel that strong why not just move?