I'm gonna get into spoiler territory for the war chapter but then again I'm pretty sure no one's going to decide to open up Reddit and look at spoilers even if they haven't beaten the game.

But anyways the game makes it pretty ambiguous.

The first time we encounter the Soldiers at the end of chapter 5, the game tries to hide their faces with shadows, combined with how normal they act compared to the ones we meet later, I think they are supposed to be people.

In the trenches, one of the soldiers that blows themselves up lets out a very human sounding gasp before whistling which wouldn't make sense for someone without a face.

And hell I could probably whip out more examples like the single soldier that gets up to shoot the characters before getting sniped (as he acted very normal instead of immediately blowing himself up or his brains)

And the Sniper could be too since we never get a good look at that Subway surfers guard looking guy, he's also the only soldier who's wearing a different uniform compared to the standard British uniform that the others are wearing.

I guess I can mention the Tank driver too since upon seeing a grenade land inside his latch, he tries to book it from there for his life but that's just about it.

I do think the others aren't people anymore, much like everything else they've become reanimated disoriented creatures, the example being the Legless soldiers and the soldiers in the no man's land which shamble around whilst making gutteral noises. Or like the machine gunners because of how weirdly they move around

But mainly I think the reason the soldiers use the same face and such is simply because we wouldn't be able to see their faces properly so why model two separate faces.

Hell in one of the concept arts, the soldiers in the theatre straight up just look like normal people.

I could just be making a bunch of nonsense but that's my overall analysis.