The DMs Guild is unlocking the Spelljammer setting for its 5e fans to create indy options for the Spelljammer setting.
It is possible to use the features that have been unlocked to reconstruct the original Dark Sun setting for options that can be published in the DMs Guild.
Use the term "Doom Sun" when you mean a 5e version of it that is publishable in the DMs Guild.
Also, DMs Guild hasnt actually Dark Sun itself. So circumlocutions are sometimes necessary.
For example, "Athas", the name of the planet of the Dark Sun setting is probably off limits. I suggest referring to a different planet called "Ashta" instead. Ashta is a planet (or rogue moon) that is tucked away somewhere in Doomspace. You decide where it is. The personal names of Dark Sun, like Rajaat, Borys, etcetera are probably off limits. But somewhat generic terms like "sorcerer kings" and "dragon" are probably fine. As far as I can tell, the "mul" race is still off limits, but a "half-dwarf" is unobjectionable.
Spelljammer even unlocks the term "Defile". So any VARIANTS of the Defile mechanic are also totally ok in DMs Guild.