The Iron Golems for unknown reason ignore and don't attack the Pillagers that naturally spawned during raid or inside of Pillager Outpost area. Even the Pillagers attacking the Golems couple times they still don't react to the Pillagers. This however doesn't occurs on Pillagers that spawned using spawn egg.

Update: Forgot to add this information. After a few seconds testing of Iron Golem reacts to Pillagers, the Iron Golems that already killed player-spawned Pillager will going to a naturally spawned Pillager then the game crash with crash report below.

Note: The Iron Golems that in the pictures below were given Bad Omen effect.