I recently came across this TED Dynamic website in association with the Technology in Education & Design Conference.
I would say that Betas can play any role in the triangle, but that there's probably a tendancy towards rescuer and victim behavior in NFs and more of the persecutor tendancies in the SJs or SPs - at least if you view it through the sexual subtypes (ENFJ & INFP Victims and ESTP & ISTJ Conquerers). I think there can be a tendancy for ESTPs to rescue and ISTJs to act as victims, but that it never overcomes their overall tendancy to strategize or be aggressive.
Anyway this website discusses ways we can shift our roles into more positive ones. Please feel free to discuss:
TED* Tools || Video Vault