Elder McConkie is correct that there are two Old Testament references to descendants of Aaron as "Aaronites." However, this is in no way reflective of the doctrines of the Church.
In his attempt to be comprehensive, Elder McConkie includes a number of superfluous articles like this one, which seem more designed to enhance the authoritative reputation of the book rather than actually confirm any point of doctrine. Elder However, McConkie does use this article to reinforce his mistaken understanding of the importance of lineage as mentioned in his previous article about the Aaronic Priesthood.
In reality, no modern revelation or significant church teaching has ever referenced "Aaronites," and this is an article that ought not have been included in Elder McConkie's book.