I have both Android Auto and Google Speech Recognition and Synthesis installed on my phone. While I receive notifications of SMS messages, I have not been able to playback there content or respond to them.
Could be various reasons for this. I will not install Google Assistant on my phone. I also do not allow either app to access the internet. My use case may not match yours, it could be that you find the right combination to get this working, but I just don't care enough to tinker