Yes. But the majority of the Ozians who are not of imperial blood and are not descendants of Lurlane are regular human. There are several races of fairies in and surrounding Oz, such as the mist maidens and Polychrome, who is a sky fairy, and since Oz is a fairy country, no one dies unless they are evil or wicked like the witches who once ruled in the Eaat and West.
Nick Chopper the Tin Woodman was once a human man made of flesh, but is now all tin. This could only happen in a place like Oz because it is enchanted with fairy magic.
Exactly. It is still on earth, but in a pocket dimension and was completely surrounded on all four sides by a desert which insulates the citizens of the Land of Oz from discovery and invasion. In the first two books, this is merely a natural desert, which is too harsh and vast to cross, and with only its extent making it dangerous to the traveler, but in the fifth Oz book The Road to Oz it is said to turn anyone who touches it to sand. In the sixth Oz book The Emerald City of Oz, the book ends with Glinda creating a barrier of invisibility around the Land of Oz, for further protection. This was, indeed, an earnest effort on Baum's part to end the series, but the insistence of readers meant the continuation of the series, and therefore the discovery of many ways for people to pass through this barrier and dimension as well as over the sands. Despite this continual evasion, the barrier itself remained; nowhere in any Oz book did Baum hint that the inhabitants were even considering removing the magical barrier that keeps Oz in another dimension.