[DrVenture]

Depending on the wheels, they could connect a hose to the shraeder valve and open it, for bleeding. With my 668M wheels and M brakes, the fronts could be done that way. I don't think the rears could.

My concern would be that any leakage gets on the wheels and brake fluid is corrosive.

I've only done bleeding during brake jobs and the wheels were already off.

Where I live they use plenty of salt on the roads during winter. I have seen similar damage on many wheels. It is usually under the clear. Since you stated they do not catch your fingernail, I am thinking that is the case here.