The Amazon Echo itself won’t actually work (at least not yet) to get notifications. What you’ll need is either a speaker that has capabilities to work as a “music player” in SmartThings. My understanding is that this speaker has both Alexa and DNLA capabilities:
I’m not too familiar with these but you can check out this thread:
If you have an Android device (OS 5.1 or better), you can use a Device Handler (LANnouncer) along with BigTalker for speech synthesis along with special chimes and alarms. I personally use this setup and I like it very much.