It would be more safe to do modeling work if the optional snapping to approximate arcs, circles and ellipses (accessible though: Rhino options > Modeling aids) is being marked in a different way than snapping to true arcs, circles and ellipses. That would give the modeler a clear indication whether the object is a true arc shape or an approximation. Currently, snapping with “Center” to either type of geometry is marked the same way with “Cen” by the cursor tooltip. My suggestion is to use “Cen (approximate)” or “Cen (approx.)” for objects that are just approximation of arcs, circles or ellipses.