A sealing surface will not go through the type of cyclic loading that a con rod or piston will go through, so it shouldn't be as big a problem.
Con rods with a scratch could fail because that scratch causes a 'stress riser', which is a point at which a crack could start more easily than if it was a smooth surface.
Because the intake manifold or SC surface isn't loaded like a con rod, it shouldn't be a problem.