Mr. Heinegg: The Croatoan/Croatan tribe was not "invented" by McMillan; instead, he researched the Lost Colony history and found evidence linking the Croatan Indians and the English colonies to the Robeson County Indians based on old English pronunciations used by these Indians.
Furthermore, McMillan was not a "politician" and far from "Jim Crow politician" as you alluded here. He led the efforts on behalf of the Indians, and was responsible for enacting legislation to officially recognize these people as "Croatan Indians", also having supported the passage of acts which established schools for them (the Indian Normal School in Pembroke).
As for "he did not bother to explain what happened to the tribe between 1587 and 1885" - he simply did not posses the data needed, as even the later historians could not unravel the mystery, based on lack of historic information during that period. However, there is a plausible evidence linking the Croatan Indians with settlers/sailors stemming from Croatia (Ragusa). There are still several places named after them - namely, Croatamonge, Croatamung Island, Croatan Sound, Croatoan and Croatoan Island, etc.
Please refer to further reading: