In checking the Carson Bent Boggs Genealogies by Q. McClung I did find mention of quite a few Millers. Some of their connections were not clear but there was a line of Millers apparently descended from Kit's uncle Robert Carson 1759-1810. This line migrated early to Ohio County, KY. The only mention of Dakota's was a Carson line yet to be connected to Kits family from a David Carson, son Robt (1762-1837), son Jackson Willoughby Carson (1818-1887) whose son Samuel B. Carson was a land agent in the Dakotas. I'd be happy to check further if you have any more details.

Doug