I cannot find an instance where a High Council specifically hires a mercenary company to do its dirty work.
However there are several times where reputable people hired mercenaries. The Merchant Mintar and Cos are just two examples.
Mintar had a mercenary escort when Tarl wounded Kazrak and took fee to repay the debt of Mintar's lost service.
And Cos certainly hired many, many mercenaries to overthrow Ar.
As for there being codes and laws for mercenaries . . . The only code a mercenary has is to the highest pay.
A good example of this are the mercenaries of Ha-Keel who attacked the Wagon Peoples under contract with Saphrar but did not burn the wagons nor slay the bosk because they were also being paid by the Tuchuks.
Same for honor. Mercenaries are shown to literally switch sides in the middle of a fight by turning their jackets inside out or changing a colored scarf because the fortunes of war now favored the other side.
So, it seems entirely feasible that a High Council would employ mercenaries . . . as long as they were assured they could out-pay the opponent.
(see new page for details Mercenary)
