ArtStation supports the Marmoset Viewer (.mview) format natively. In Marmoset Toolbag 2, click on File -> Viewer Export to start the process.
Currently ArtStation limits the viewer file to 15MB. This is to ensure fast load times and allow the viewer to work across as many devices as possible.
For more information about the Marmoset Viewer, please visit Marmoset's official documentation here.