Please read the manga. ( not meant as an insult here😅)
There are no "Gods". There are individuals who are seen as such for a variety of reasons: "Sword God" Ryuma, "God" Enel, "God" Usopp, the celestial dragons etc...
Nika was seen as a "God" by the slaves who remembered being freed by him.
No, Nika is legitimately a god. That's what the DF implies as it is classified as a mythical zoan.
While joyboy, the previous user of Luffy's DF, was a real person, there's nothing that suggests that Nika was ever a real person.
[automerge]1649360641[/automerge]
I think there could be at least 1-2 more god fruits that bestow the powers of gods from the one piece pantheon.