Chris,
From the links below I would say Hollywood took creative license.

http://www.incallander.co.uk/rob_roy.htm

http://www.rampantscotland.com/famous/blfamrobroy.htm

http://www.isidore-of-seville.com/robroy/

http://www.lordbothwell.co.uk/robroy.html

I see that you are related to the Malcolm Clan. Tell me more, cousin!