The 1983 boxed set has lots of clear-cut Good and Evil.
With the caveat that different people have played Greyhawk in a different way ...
I think this goes to the difference in how people view "morally ambiguous" within different genres, and how it influenced different settings. The backdrop of Greyhawk is very much with the idea of some of the S&S and pulp fantasy novels that Gygax enjoyed. Not to be too reductive to the genre, but you could often have a
world with absolutes, and
morally ambiguous characters navigating it.
This is reflected in the design of early D&D, with an emphasis on alignment (even with alignment languages), a muscular neutrality, while keeping ideas of real good and evil as well (reflected in classes- Druids, Paladins, and Assassins).
Greyhawk had real good, real evil, and even "real" neutral. Just like a lot of its influences. And the protagonists (the PCs) could align with that, or be independent of it, just scratching out what they wanted (a selfish moral ambiguity, which often ended up opposed to evil, a kind of darker Han Solo

).
This is in contrast to more traditional "High Fantasy" inspired settings such as FR or what we now think of as morally ambiguous settings, where it's all, "They're not really evil, they just disagree with you." That isn't traditional Greyhawk. Iuz doesn't just disagree with you. Iuz is evil.