Pocetty should be an americanisation of Pocetti. Possibly Pacetti is an americanisation of Pacetti that could come from "pace" an old first name. Italian surname have a long story, usually about for centuries at least. there is an evolution... at the very beginning they had a dialect pronounciation,then converted in latin an finally in Italian. It is really quite complicated.
At the moment Pocetti still exist in the italian region of Abruzzo. Some Pocetti migrated to USA. In Italy now live about 100 people called Pocetti: it is a local surname, mainly from a little municipality called Fossacesia, at the moment a sea resort near the Adriatic Sea.
It could be an old first name coming from Puccio or Poccio, Pocio it is a variant. I am trying to guess.