"Now on to how the member is stressed. The spindle is a cantilever beam and the maximum moment is at the root of the spindle, tapering off to zero at the point where the outer wheel bearing exerts a force on the spindle. If the vehicle is rolling straight the upper side of the member is in compression, which does not affect the "stress risers". It's only where the tire is trying to tuck under the car that there is a possibility of this area being in tension, and that tension is opposed by the weight of the car. So the amount of tensile stress in that area may be quite a bit less than imagined."

That tuck under you mention, in a high performance application can occur under braking, in a high g turn, and depending on other suspension variables, could be 70%? of the weight of the car, and then add the potential dynamics of bumps, etc, I think the loads can be higher then imagined. Failure will likely be at a point of maximum stress, not over time, when subject to only the rolling weight of the car you brought up. Are we also assuming all the rust the OP is asking about is only on the upper surface pictured that under ideal normal conditions as you described iis n compression, and not underneath? We are also assuming, I believe safely, the COG on the car is above the centerline of the spindle, and therefore the "tuck under" mention helps to reverse load the spindle.

Bottom line ANY surface irregularity is a potential stress riser, all should be avoided, the consensus here so far, which I agree with, in the OP's case, its an insignificant stress riser. Why are beating this to death again?