What an interesting question! Two authors with very distinct styles, indeed. I think that both authors express similar IDEAS and THEMES, but the way they deliver these ideas (another part of style) is not so similar: however, this is worth exploring. In Alexie's The Absolutely True Diary of a Part-Time Indian and Morrison's Song of Solomon, two young men (Milkman and Junior) experience loss and struggle to discover their cultural identities, and both authors lend voice to the characters. However, Morrison writes in third person and Alexie's Junior directly addresses the audience in first person. Also, Alexie uses a great deal of humor and hyperbole to express theme of oppression, while Morrison tends more toward the ironic, while also embedding historical allusions that deserve careful analysis. Also, the narrative structures are very different. Alexie, while anecdotal, tells a linear story, while Morrison's tale weaves in and out of past, present, and future. As for language, both authors use quite a bit of dialogue to develop voice, but internal monologue is more prevalent in Morrison. Figurative language of simile and metaphor are similar, I guess, but overall, I think the emphasis should be on stylistic differences on similar themes. One more thing: Conflict between Rowdy and Junior could be compared to Junior and Guitar, particularly at the end of both novels. Hope that helps. Again, I am treating style as form more than content.
I would say that one particular stylistic similarity between both authors is their articulation of what it means to be "different" in a particular social setting. Both authors are animated by a particular and specific articulation of an experience that might lie outside what is considered to be "the norm" in social interaction. This exploration of voice and enhancement of individual narrative proves to be something that unifies both authors. For example, Alexie in "The Diary of a Part-Time Indian" explores what it means to be Native American in modern social and adolescent settings. How does one straddle what it means to be "different" in such a setting? Morrison explores what it means to be black in different contexts and settings. For example, the exploration of Sethe's voice in "Beloved" is one that straddles race/ ethnicity, historical context, and psychological identity. In this light, individuals begin to understand emergent voices that might have been marginalized as narratives which take center stage through both of these writers' styles.