Yup, Lupa already fills this role.
Here is her flavor text: "A spectacle and
executioner, Lupa is often brought into the arena to finish off foes who have been condemned, or to rouse a crowd when their interest is flagging.
Crushing the heads of the fallen with great strokes of her hammer, or toying with opponents by incorporating elaborate flourishes, she ensures that even the most lackluster opponents will be drawn into a great show. Adept at creating a captive audience, Lupa ensures that the crowds always leave satisfied."
http://arenarex.wikia.com/wiki/Lupa