Definitely. Greyhawk really is the "implied setting" of D&D. You could have Vecna, Kas, St. Cuthbert, valley elves, dark elves, the Invoked Devastation, etc. on any map. if you played a home brew in 1E AD&D, you could feel kinship with Greyhawk. Greyhawk isn't generic D&D -- it's the Platonic ideal of a D&D setting.
Planescape is but one image of the Great Wheel that's part of Greyhawk.
Nentir Vale is an attempt to recreate the magic of Greyhawk, which is doomed to be just a reflection.
Even the Realms, despite not being conceived of as a D&D world -- by becoming a D&D world and importing things like drow -- shows Greyhawk where it rubs thin.