What's the difference between active dry yeast and instant yeast?

Here is a brief treatise on baking yeasts that may answer your question: http://www.kingarthurflour.com/recipe/yeast.html

Basically, instant yeast (aka rapid rise) can be used without hydrating it first.

Feeding with sugar ("proofing") isn't necessary in either case, basically a holdover from days past, a test to "prove" the yeast was still active.