I've come to believe that the Robert Elliott in the Draper collection papers who interacted with Oliver Pollock and Dr. Croghan is the Robert Elliott who settled in Louisville KY and whose daughter Sarah married Robert McConnell. I have yet to track down copies of the Draper papers, but an excerpt from History Quarterly contains the following commentary on the collection:
"The Captain Elliott and wife were evidently Robert and Mary Elliott, for in the records of Jefferson County, Kentucky, are the records of the marriages of. Rob't McKonnell (sic) and Sarah Elliott, April 11, 1799. (book 1, pg. 33)"