Yes, there is no DISM or WUSA available for Updating Windows IoT Core. Starting with 1809, the device will by default scan for OS updates. For older releases prior to version 1809, device can be set to receive OS updates only directly from Microsoft by using IOT_GENERIC_POP feature in the OEMInput XML. IOT_GENERIC_POP is deprecated in Windows 10, version 1809. There are several ways to manage the updates.
- Using Update APIs(Windows.System.Update)
- Using Device Management
- Using Azure IoT Device Management
More details, please see this document.