I know this has been stated before that Mobs ignore the "friendly fire" option of a team (they don't target players in their team, but they still can hurt and get hurt by players of their team), see https://bugs.mojang.com/browse/MC-46956.
BUT since shulkers are, as far as i believe to know, intended to be able to work as turrets etc., i don't think that they should be able to hit Players of their team. they don't attack them actively, but if a projectile hits the Player of their team, they will still take damage and get the levitation effect.