Jan, I'm not sure if that would help as the import toolkit only works on the web server and I don't think their admin may have access to the server.
Dilip, in this case, you may want to just create a ASPX page for import data using API to a matching custom table in the CMS. Assigned that ASPX through Modules app so admin can have access to this app page within Admin UI. After the import, they can check out the data in Custom Table (Data) app.