If it is a personal/non-commercial mod, I don't see why not, but I think there would be some issues with that. They are not the correct scale and resizing them would probably be messy, and they have an alpha channel. Some of the slight blurring around the edges would be lost of you did a curves adjustment to the alpha channel, or worse they would become solid black pixels.
And yes, they are *intended* for AB.
Regarding the lighting, they used the old internal render engine, which is no longer available in the latest Blender, but in general, the material is a perceptual 50% gray diffuse Hex #808080, and the lighting is a simple sun lamp directly straight down at .75 power, and environment lighting of .25 (.75+.25=1), so that the results would be near 50% gray. Then an Ambient Occlusion pass is composited on in Multiply mode. Then in Gimp just brightness and contrasted until I like it. Really that is an over simplification, but the guidelines are correct.