How is it that Borkul the Beast is a Forsworn? There are two Orc strongholds in or near the Reach, but how does an Orc fall in with the Forsworn? Is there an in-game explanation?
I don't think he's actually a forsworn... or at least, he wasn't until he got into Cidhna Mine. If you talk to him about his prison time, he answers:
Guards brought me in about 12 years ago. Was running a good group of bandits up until then. But these Forsworn. They're nothing like the men I cobbled together. They're real killers
The way he says they instead of us, suggest that he's not one of them... he's just Madanach's bodyguard.
If you release the prisoners, he will join them in Druadach Redoubt, to start his life anew as a part of the forsworn, according to UESP