it is my theoretical belief that the nine are a secret group of 9 associated with the vex or some thing that has a plan for the univers but needs time. so the nine empower both us and the enemy with powerful weaponry to keep us guardians focused away from their master(s). prime example is xur their agent who gives up weapos and armour. also it was the nine who released skolas and gave us guardians that massive fiasco to deal with