I have been pondering this a number of times. Dramatica positions character traits in relation to the story's goal. Certain thriller/adventure genre films often have, besides a top villain, the hitman or stalker chasing the protagonist. They're chasing the protagonist through the entire story, firing weapons, etc. following orders from on high. I have been categorizing them as sidekicks because of their "support" trait. They are supporting the top villain.
Now I think about this in relation to the protagonist's effort to achieve a goal. These hitmen are actually countering the protagonist's mission. Where would they fall typically in the Dramatica character chart, because they no longer seem actual "support" characters defined by the protagonist's story goal?
The Contagonist is a separate issue. This is usually a prominent henchman of the villain who screws up ("hinders") efforts of both the protagonist and antagonist. Example: Emil Muzz in "Dragnet". Darth Vader in "Star Wars". Walter "Dickless" Peck in "Ghostbusters".