I tested guns on a couple of Zombies with a health bar mod and the Armor and Helmets on the zombies that naturally spawn have no effect/give 0 protection.

Armor
(Video is inside of the ZIP, couldn't upload the MP4 itself)
2020-11-11 19-32-53.zip

Helmets
(Video is inside of the ZIP, couldn't upload the MP4 itself)
2020-11-11 19-37-48.zip

Again, I didn't use all weapons, could be this one specifically, could be the certain armors, not sure. But still worth looking in to unless this is intended.

Nope, the CD Armor that the zombies now spawn with don't seem to give extra protection against guns.

That’s intended, CD armour only protects against infection and bleeding.

Oh gotcha, so are players meant to be able to get items like Vanilla Armor this time around? Is that why all of the guns have recipes and whatnot?

Precisely.

Are you referring to vanilla armour and helmets?