In the Settings app on iOS (9.3.2 and many earlier versions), you can go to General -> Storage & iCloud Usage -> (iCloud) Manage Storage and see icons under "DOCUMENTS & DATA" for any apps like Numbers and Pages which have stored documents in iCloud. I have a shared ubiquity container that shows up here but does not have an icon. (It displays a default icon.)
Is there any way to create an icon for shared ubiquity containers that will show up in General -> Storage & iCloud Usage -> (iCloud) Manage Storage that will show up under "DOCUMENTS & DATA"?