I actually came across another group which seemed to be only semi-aggressive or defensive. They patrolled a small strip of road in the mountains, jogging back and forth, not minding me except for saying "That's close enough." when I was within a few feet of them. There were also a few corpses of a group of Orc hunters on the road.
And I'm with msxyz. Helping Madanach should at least lead to some sort of a personal cease fire between the Forsworn and the player.
Forsworns have the same AI package of bandits (and beasts): there's a 'safe' distance above which the NPCs will throw a verbal threat at the player but won't become hostile (in case of beasts, they will rsend other aggressive signs).
As for the Madanach, the whole neutrality issue (or lack of) can be easily changed once the CK is out. All you need to do is to add a line to the script governing the "no one escapes cidna mines" quest. Unfortunately it won't be retroactive unless there's some global variable that states that Madanach escaped AND survived.