It should work. It's hard to say more without more information. Although I think there's an iOS issue where the app icon is cached the first time so won't be updated. So if you exported with the default icon, tested it, then changed the icon and exported again, iOS will keep showing the old icon. I think you have to uninstall the app, reboot the device, then reinstall the app, to get the icon to update (or something like that).