The debate over whether George Costanza is Jewish or Italian reminds me of a scene from the Marx Brothers' movie "Animal Crackers".
A cultured art critic at a posh party is thought by Chico to be a Hungarian immigrant he knew from the Lower East Side called "Abie the Fish-Peddler". Chico taunts the man until finally the fellow admits (in private) that yes, he is Abie.
The implication is the man is Jewish and has been breaking into high society by posing as a non-Jewish European aristocrat. They have this exchange:
Chico: Heh, heh, so Abie, how long have you been 'Professor Huffington'?
Professor: How long have you been Italian?
My guess is that George Costanza is just as Italian as Chico Marx.