I just thought about something...

There could have been a corrupt "Bosshunters Guild" equivalent, but clearly that doesn't exist. Probably because there wasn't an original grandmaster of that faction, so the art was lost after the war. So no pirates.

As is mentioned in some of the quests, there are several other guilds that existed in the keep: Antellion Guard, who took care of the Antellion (the relic which was likely responsible for Masteria's disappearance after Crimsonwood fell), and the bosshunters as you mentioned. I wouldn't be surprised to see counterparts of these two inside the keep.

Also, the key to the 4 Crimsonwood guilds is that they're mixed disciplines: While they have an influence of one class, they're all made up of attributes of two classes.
1. Firebrands (and by extension Flamekeepers) - Magic and Archers
2. Windraiders (Windreavers) - Archer and Thief
3. Nightshadow (ShadowKnight) - Thief and Warrior
4. Stormbreaker (Stormcaster) - Warrior and Magic

Ever wonder why it's a Flamekeeper Cordon, after an archer glove? This is why. The whole concept here is that everyone in Crimsonwood mastered 2 different classes.