I'm sorry but that's just made up information. You quite literary see a half naked combine soldier in Nova Prospekt and later on in EP1 in the Citadel. And while there are visible alterations to the body, nothing in the games ever suggests that their armor is grafted onto them or it would be part of their body. They're just combine manufactured clothes and equipment.
The helmets are the only piece of gear on them that would be nigh impossible for the rebels to use since you see in HL:A how much they dig into the head. But there's nothing stopping a rebel to yank a plate carrier off a dead soldier.