Did you already go skiing with your sling? How was it?
As everyone mentioned, do your best not to fall on it. If you do fall toward that shoulder try to go down in a rolling motion instead of sticking out your arm. With your arm in a sling it would be hard to stick out your arm anyway. There are braces which you can wear to help stabilize your shoulder but really the biggest thing that'll help is falling properly.
As for poles I think they'll be fine but don't use the straps.
Just be aware of how your shoulder dislocated and avoid those arm positions. With some luck and caution you'll be fine :).