As a Sicilian surname (from the province of Palermo), Scimeca might also have an old Arbëreshë or Slavic origin, just as a lot of other last names from Palermo area do (you can check the history of the Arbëreshë immigration to Italy at
http://en.wikipedia.org/wiki/Arb%C3%ABresh%C3%AB_people).
In this case it might come from the Slavic surname Šimek (pronunciation: Shimek), which is just a pet form of the personal name Šimon (English: Simon) through his short form Šime + the diminutive suffix -ek (
http://www.ancestry.com/facts/Simek-name-meaning.ashx).