"Beat! Beat! Drums" stands as a testament to Whitman's desire to crush the Southern rebellion absolutely. But there is no mention of emancipation or slaves within the work. I think that Neely's assertion stands, at least nominally, for Whitman does not make an explicit statement on slavery or the Emancipation Proclamation in the work. But, I hesitate to say that Whitman did not care about Emancipation at all. When looking at works of Whitman's, such as "Leaves of Grass", that predate the Civil War, then it becomes clear that Whitman believed firmly in justice and liberty and hated anything that stood in the way of these liberties. In fact, Whitman repeatedly mentions the role of poets in the battle for liberty. He believed it was the responsiblity of artists to expose the inequities and injustices of the world, to help to spur action and be an example for people to follow.
"Beat!Beat! Drums" holds none of this sentiment. There is no mention of liberty, freedom, or the obligation of poets to expose the actions of the unjust. Instead, the poem is an ode to the destructive power of war. Whitman encourages war to run through the country with no regards to anyone. He wants there to be no peace until victory is won. Let no farmer work, let no bridegroom have peace, let no one be comfortable while this war wages.
At the same time, I do not find this work to be the work of a "mystical nationalist", if only because reconciliation and union are not big themes in the work. This poem is a song praising the destructive power of war and asserting the necessity for sacrifice and ruthlessness. When Whitman says that no one shall practice their everyday routine, it is a message to the world that says everyone must sacrifice for their side and fight. At the same time, it exhorts the forces of war to disrupt the lives of the enemy, to destroy their lives. This is not a poem that expouses reconciliation and common brotherhood. This is a poem that demands the absolute destruction of not only the enemy's army but of the enemy's way of life. This poem does not carry the sense of someber, tragic necessity that infused the speeches of Lincoln like the Gettysburg Address or hist Second Inaugural. Instead, Whitman succumbs to an all consuming bloodlust that overrides any sense of "mystical" nationalism or reconciliation.
So, while Whitman does not explicitly mention emancipation in this work, he also does not mention or subscirbe to what I would describe as a "mystical" nationalism. This work is an ode to destruction, death, and interruption. There is no overriding sense of nationalism here, only violence. Whitman is caught up in the moment of war, blind to the greater contexts, revelling in the simple chaos and destruction that accompanies it. So, I must respectfully agree and disagree with Neely's assertion, at least in the context of this one particular work.