Silvio asks Tony if he "went to school with a guy named Artie Bucco" in the pilot so I don't think Silvio was friendly with Artie. Silvio's character was slightly altered for the main run of the series though, but I'll still consider what happened in the pilot as canon. The thing to remember is that many of the people in Tony's crew (Puss, Paulie and Silvio) are older than Tony so they wouldn't have necessarily known Artie. Ralphie might be the same age though as Tony.