In reply to dutybooty: I have seen people skiing up (or actually down), either of Castor or Pollux in July.
But in general in Summer you are much more likely to have the surface turned overnight to hard ice in the morning, then to complete slush (or "Soup" as the French call it), in the afternoon, neither is particularly good for skis, while ice is just fine for crampons. So there is no need for the considerably increased complexity of skiing in Summer, while in Winter they (or, as much discussed, snowshoes), are indispensible.