D'Imperio could be a variant of Imperio or Imperi, last names that derive from the word "impero", empire. So this surname comes probably from a nickname. The D'Imperio are spread in Southern Italy, especially the provinces of Foggia, Bari and Campobaso.
Many immigrants in USA came from the area of Campobasso (seewww.ellisisland.org
Zampino is also typical of Southern Italy, di could be a variant of ZAMPA, "paw" a word that sometimes is used to indicate also human hands.
This surname comes probably from a nickname difficult to explain.