Welcome to the forum, @olivern.
Depends. Would it render faster than which alternative? From your other questions, I infer this to be a comparison between macOS and Windows? The OS really is not important here—what matters mostly is the graphics card, as well as to a lesser extent CPU performance and available RAM.
ImageJ’s classic 3D rendering plugin, the 3D Viewer, leans on Java 3D. The new one under development, SciView, leans on OpenGL and also has a new Vulkan backend via its backing Scenery library. So really, this question is just about comparing OpenGL rendering et. al across graphics hardware specs.
No, ImageJ does not offer any CUDA-based acceleration. And no one is working on this yet, to my knowledge, at least not in the general case of volume rendering.
Probably not by the definition of “fully” which is desired here. But yes, you can import DICOM files and then export meshes using the 3D Viewer (File Export Surfaces STL menu items).