A scrapped concept, but a disturbing one nonetheless!

First, this is concept art. Not canon. Second, that's not a human, that's a reploid (notice the beret flying off)

Not really. Most of the resistance soldiers were Reploids that fled from Neo-Arcadia. So its more whatever fluid is in Reploids that's like blood
Ciel might be the only human in the resistance if my memory is right. We don't see any other humans till Zero 4.

Now it makes too much sense for them to bleed.