The beauty of SmartThings is that everyone can work together to create devices and codes, but the short answer is: No, the Ecobee 3 is NOT officially supported (I asked SmartThings support and they confirmed this)
The long answer is below:
@StrykerSKS has been working hard on free Ecobee integration and it’s now live and works great (yves is not free, but has a lot more integration).