I've got a Little Giant Water Wizard and it does get pretty warm around the upper aluminum casing. I only got to use it a handful of times before the seasons changed and it wasn't needed, but I think keeping the sump water shallow reduces the heat transfer to the water/ice. Mine will draw down to an 1/8" so a couple inches of water/ice work fine, but I only use it for the last 10 or so degrees of cooling and it doesn't run for too long.
If you are going to use the pump for the whole cooling process I suspect you'll need a lot of ice and a larger volume of water.