Most IKEA devices now use standard Zigbee 3.0 and add just fine to smartthings. They are very popular in the community.
The exception is the various batterypowered button devices. Those are definitely trickier. 
Which specific models were you interested in using with smartthings?
Anyway, to answer your question, smartthings does not provide MQTT integration as an official feature. Some people are using it, but you have to set up a separate server device to act as a broker, and it can get pretty complicated. But doable. See the following topic: