You seem to be thinking of either Spitter Zombies or Corrosive Zombies.
Acidic Zombies have no ranged attack, and simply spray acid in the area around them when hit or when their corpses are smashed (butchering works fine).
Spitters fire a large splat of acid from relatively close range, but have a long cooldown time and do not spray acid when hit (though they still spray when you smash their corpses)
Corrosive Zombies are large and tough, and fire a precise single-tile acid attack from relatively long range. They also spray acid when hit.
Assuming we’re talking about the basic Acidic zombie, personally, I think they’re fine. They’re barely more dangerous than a regular zombie to ranged weapon wielders, and while melee fighters are likely to get hurt when dealing with them, this can be minimized through proper tactics and preparation. I’d rank them a little below spitter zombies in terms of overall threat level, unless you’re fighting a lot of them at once with pure melee, in which case your best option is to run and find a better way of dealing with them.
If I had a recommendation, it would be to add an “Are you sure you want to do that?” prompt when attempting to (s)mash an acidic, spitter or corrosive zombie corpse. God knows how many times I’ve done that by accident when cleaning up a recently swept area without looking too closely.
