I'm going to get a bit picky here. An external character like this could be brought into Daz Studio and rigged there so that it could be posed. Basically, you'd have to bring in the mesh create a skeleton (or copy one in) and then do the weight painting. (In theory, you could just bring it in as a pre-rigged FBX, but Daz Studio's ability to reliably import "foreign" formats is not good at all.) Doing that, however, will not make it a G8F. It would make it a completely new and separate character, unrelated to any of the existing Daz characters.
To be one of the Genesis variants, and have Daz Studio work correctly with it as such, requires that you use the existing mesh for the corresponding Genesis generation. Every single G8F character, for example, uses the same mesh, just with the vertices moved around a bit. (Or a lot.) The fact that the mesh is identical (same vertex order, same polygon definition order) is critical, because it affects a number of aspects of how Daz Studio works - clothing "auto-fit", for example. So the above technique might give you a poseable figure, but it wouldn't be (easily) able to wear any G8F clothing.
Now, if you really wanted a G8F figure, what you'd probably have to do would be to take the external model and a G8F model into Blender and then resculpt the G8F model (without adding or removing vertices) so that it matched the model in question. Once you'd done that, you could then re-import the resculpted G8F mesh into Daz Studio and use Morph Loader Pro to set up the new Padme shape as a G8F morph, just like any of the other character morphs. Then you'd "only" have to deal with getting the materials into all the correct UV mappings for G8F.