If ships are in port, the shops will be open. I wouldn't call St. Thomas shopping incredible. As with many things in the Caribbean these days, it isn't as good as it used to be. Prices are set and their is little or no negotiating.
If you dock at Havensight pier you will have an open air shopping mall right there, literally a minute or two walk from the ship. These shops also have a presence downtown, so you'll see the same things in both places.