Yes, it is. The James and Younger gangs disguised themselves as cattle buyers when they raided the bank in Northfield, Minnesota in 1876. Part of the disguise was to wear dusters over their clothing - the sort of thing a businessman would wear over his suit to keep it clean while inspecting cattle on horseback, and then visited the bank. But this implies that the gang members dressed in suits, or otherwise the disguise wouldn't make sense. In the 1972 film, The Great Northfield, Minnesota Raid the James and Younger gangs ignore this bit of logic and wear dusters over their dirty cowboy clothes. In the later film The Long Riders  the gang members actually do wear suits beneath their dusters, for the most part. But that hasn't kept the duster from being shown on cowboys in trail-grimed clothing ever since.
Actually, one of the sharpest send-ups of the outlaw image of dusters comes in the Cohen Brothers film, Raising Arizona , when modern-day bank robbers John Goodman and William Forsythe put on dusters over their street clothes before pulling a heist.