I'm using the amalgamation mods with Supersoldiers (Core), the description of Will over Body in the Ninja tree mentions a 50% will regen/per turn. I didn't see this happen during the mission. I checked the X2Ability_NinjaAbilitySet.uc and although there is a mention of //Template.AddShooterEffect(new class'X2Effect_WillRegen'); the effect doesn't appear to be defined further. I'm not a coder so I apologize if I missed if it's defined somewhere else.
I think the Nanosuit also mentions the 50% will regen/per turn and it also didn't appear to be working.