A primal/eikon is a manifestation of Paragon-inspired dilusions and a crapton of crystals. The 12 would be very good candidates for such acts as already mentioned with the Little Ala Mhigo quests involving such matters. While those who have been under Imperial occupation may have been more inclined to avoid summoning what would now be perceived as a false god prior to the death of the first Garlean emperor would almost be encouraged to summon Rhalger to some twisted extent by the new emperor given his obsession with controlling the Warring Triad. Which I assume is where his son will come into play, given the Yoshida's mentions of said son's ruthless demenaor.