I put over 100 hours into this game, I have over 100 hacked orcs (feel free to look up my forts in game - I stopped playing because hacked orcs killed the game for me,) I like many players figured out how to kill them, but when I first started playing and looked for strategies, I did not find any viable solutions. Many solutions were gear or prestige point dependent, or theoretical and would just not work.

I will tell you the simplest and easiest way to kill a hacked orc so you can break them and start your own army. This does not depend on gear, level or prestige, and barely involves combat.

All you need is a marksman bodyguard with Sniper Shot and the epic strength trait. Summon the bodyguard where he cannot get into melee combat but has a clear line of sight on the hacked orc. In a throne room this would be one of the ledges, outside the fort, this would be a tall building without lower ledges. Then you stand back and let it do its work. At level 80 the marksman can break them in 3-4 shots. If you are in the middle of a siege you will have to assist by clearing trash around the hacked orc, either shot the enemy orcs to help your bodyguard focus, or kill your own orcs to prevent the hacked orc from healing (he will heal a little with every enemy killed.)

When the hacked orc breaks, use shadow strike drain to safely dominant it.

In a siege use your hacked orc to get other hacked orcs by equipping a ring with +50% damage to allied orcs. This will give him a significant advantage over other orcs and will allow you to build your hacked army quickly (relatively quickly, hacked orcs fighting each other is slow, painful, and buggy lol.)

Good luck