(!) St Sabrina, despite having a white priest, is an African American church in term of its membership and orientation. True, it is part of a larger church whose leadership is not predominantly black, but the same could be said of the Trinity United Church of Christ. (And if it be objected that the Catholic Church is more centralized than the UCC, an obvious reply is that Father Pfleger certainly didn't prove to be a mere tool of the hierarchy and indeed was always getting in trouble with it.) An Obama who worships at St Sabrina will still be a black person living in a black-majority neighborhood and who worships in a predominantly African American church. Nor do I see why he would be less likely to marry an African American woman--he met Michelle Robinson through Sidley & Austin, not through the church.
(2) I think the election results of 2008 and subsequently show that the argument that Obama (because one of his parents was white or because he is not the descendant of slaves in the antebellum South) is not "black enough" was never taken seriously by most African Americans. (BTW, Alan Keyes had already tried more-African American-than-thou against Obama in 2004 with no success.)