Yes, Gaggi is based on Joey (Doves) Aiuppa. "Artie Piscano" was loosely based on Carl (Toughy) DeLuna, a KC mobster. "Vincent Borelli" in the film was loosely based on Nick Civella of KC.
Despite Gaggi being based on Aiuppa, didn't he resemble Accardo a lot, too? Especially the way he wanted to keep Vegas low key? Was Aiuppa as adamant about things being low key? Gaggi seems helpless when it comes to Nicky Santoro. He knows Vegas is turning into a disaster and that it's mostly because of Nicky starting operations that he was never supposed to start in the first place, but there's just a shoulder shrug response to it, until he kills him, of course, but by then it's far too late. That helplessness seems to reflect Accardo's adviser status during this era as much as anything, imo.