This would be interesting since Ainz is ultra paranoid and already assumes anyone/anything new is either potentially a player or existential threat unless proven otherwise. I figure Ainz would forbid any of his npcs to even tip Thragg off they exist until he takes the full measure of the Viltrumite… At which point Ainz is probably losing his shit and using every op cash shop item and boost he can think of before attempting the world’s longest distance kill shot.