Unfortunately no, you have to choose one or the other.
IKEA Tradfri devices do not individually connect to HomeKit. Instead, they rely on the IKEA tradfri gateway.
But since the device cannot belong to both the IKEA Tradfri gateway and the smartthings hub at the same time (you have to choose one or the other), when you join it to smartthings you lose HomeKit. 
If you have fairly strong technical skills you might be able to use a system called “HomEBridge“ and an additional server device to join it to smartthings and then bring it back into HomeKit again, but that gets pretty complicated. You can talk to people in the following thread if you want to find out more about that method:
[RELEASE] Homebridge SmartThings v2.0
At the present time, smartthings does not offer official HomeKit support and it doesn’t look likely that it will anytime soon.