For people trying out the database service on http://cloud.oracle.com, data loading got 1 step easier. Before this, there would would have to be an APEX user created with roles granted. While this still will work, now you can simple use the cloud user created at signs ups. This is the administer's login created in the initial welcome emails.
To setup a new user in the cloud that allows data loading simply launch the IDM console from your service and assign the Database Developer or Admin role to that new user.