Most Native Types Languages require each DTO to be uniquely named since most languages don’t have namespaces with equivalent semantics to C#/.NET (neither does F#). So to maximize the accessibility of your Services each DTO should be uniquely named (it also causes issues in other ServiceStack features requiring unique names).
Relying on language-specific features like namespaces works against web services interoperability, makes the generated DTO’s more verbose, uglier and harder to read and is contra to the GlobalNamespace feature which strips all DTO namespaces under a single namespace - hiding the complexity of the server namespaces by presenting them under a single namespace view, making it easier to integrate into Client Applications.