Spirit Workers can be damaged
Playing HoG level one, I noticed at least 4 different permanent Spirit Workers lacking some portion of health. I healed them, but they were found damaged again. It also seems they lack the Worker Regen ability. :P
Game Version:
Steam Public
Platform:
Windows
Confirmed with lead designer. It is intended that spirit workers should not be able to be attacked. However they should not be able to take damage.
I tested Lava and it can confirm that lava does not damage spirit workers. They also cannot be damaged by AOE however I believe that it is possible for a Spirit Worker to be directly hit by a projectile intended for another target.
This is being changed for the next patch.