Actually the southern black ferries that shod horses were very highly respected and needed.
I would have expected it on both counts, first that the blacks who were smiths would be more likes tradesmen even without their freedom, and that the whites who had been smiths were already having been forced into the infantry simply to keep the number of warm bodies up.
By the same token, a black who could smith would be the epitome of what Booker T. Washington would later have praised as the first step up from slavery, the man who had learned a trade that the white people needed to use and would be willing to pay for.