Ikea tradfri bulbs Connected to the IKEA gateway will not be visible to smartthings. Unlike Philips Hue, there is no integration available for the hub. You have to choose one or the other, not both.
To use IKEA Tradfri bulbs with Smartthings, you either have to join them directly to the SmartThings hub or you have to use them with a hue bridge.
Note: IKEA bulbs previously connected to the IKEA Trådfri Gateway must first be disconnected from the Gateway before they can connect with the SmartThings Hub.
If you want to get a gateway solely for the purpose of updating firmware, you can. Some people have done that. But if so, each time you want to update firmware you have to first reset each individual device so it is no longer connected to SmartThings, then connect each to the IKEA Gateway, do the firmware update, reset each individual device again, and then reconnect each to the smartthings hub.
An ikea Device connected to an IKEA gateway cannot be used with smartthings at this time.