well, as with all things U2... the Daddy could mean, literally, your father. But it also can have a spiritual meaning. That is, Daddy is God. Daddy could also be a nickname for someone... basically any way you want to interpret it lol
"Daddy" could be any paternal/patriarchal figure, imposing rules on someone, even in a kind way--the sort of rules that you simply have to break to get anywhere.
Yeah, but he did used 'daddy' in "Crashed Car" and I believe I read one interpretation saying that that song was about God too. So, 'daddy' in SATS could be God as well.