My dog gets red, and sometimes bloody marks on what I call her chin....and I think that hers are just from toys (irritation). The ingrown hair explanation sounds right though. Let us know if you find anything out.
Could be an ingrown hair. I had a dog that was allergic to plastic, I changed all his bowls to stainless steel and his face didn't break out anymore. He had quite a few, his chin, jowls, whisker pads, all were affected. It was pretty gross.