Summary
Zoglins are harmed by the Instant Damage effect and healed by the Instant Health effect, despite being undead mobs.
How to reproduce:
Spawn a zoglin
Throw a splash potion/lingering potion of harming at it.
-> It takes damage ❌
or
Spawn a zoglin
Throw a splash potion/lingering potion of healing at it
-> It doesn't take damage ❌
Seems like they aren’t considered an undead mob on bedrock. This should also mean that they aren’t affected by smite and swim in water and lava.