Could one use salt to clean their skin, of microbes, instead of soap?

Well, you could try this - I bet it would make an interesting science project. Offhand, I would not expect this to be the case, though. The reason that soap works isn't so much that it kills the microbes; it's more that it makes it hard for them to 'hold on' and they get washed away by the water. Salt (as far as I know) doesn't have this sort of "break them loose" property.