When a Pillager shoots a Vindicator by mistake, the Vindicator will turn aggressive and begin attacking the pillager, similarly to how other monsters do when accidentally shot by skeletons. However, since illagers aren't supposed to attack each other, the Pillager won't retaliate when attacked by the Vindicator. I haven't tested this out with Evokers, Ravagers, or Witches yet, so I would check for those too.