Quote Originally Posted by Vivi_Bushido View Post
Q8: Is PvP materia useful in Frontlines?

A: I don't think it has ever been tested on ilv70 accessories.

Although even if it did, I would image that it wouldn't be worth it since you would be missing stats by using anything below the item sync.
After testing, regular materias are not taken into account, wether on ilvl 90 or ilvl 70, in frontline. I did not test PVP materias.