If anyone had issues recently where icons didn't make it into your app catalog when you added them from VPP, here's a MySQL query that will fix all the broken icon images in Self Service:
UPDATE `mobile_device_apps`
INNER JOIN `vpp_mobile_device_app_license_app` ON `mobile_device_apps`.`itunes_id` = `vpp_mobile_device_app_license_app`.`adam_id`
SET `mobile_device_apps`.`icon_attachment_id` = `vpp_mobile_device_app_license_app`.`icon_id`
WHERE `mobile_device_apps`.`icon_attachment_id` = -1;