Possessed Workers are UAC workers that have been mutated by the Lazarus Hellwave.
Possessed Workers have a different face than the Possessed Scientists; their left eye socket is completely empty, while the right one is covered by skin. The most notable trait is that these creatures are missing their left arm.
Possessed Workers are often encountered alongside Possessed Scientists, making up hordes of the Possessed altogether. Despite having a different model, they have similar stats as the Possessed Scientists. However, their attack is slower, since they only have one arm.
Possessed Workers are referred to as uac_security in the game files, which suggests that they are UAC security personnel.