Hey there Chris_R,
I apologize about the late response, thank you for being patient! Were you able to find out the answer to your question? If not, I'd be happy to help out! So, you are able to add a Chromecast with Google TV and a Google Nest Audio into the same speaker group, however, if you do so, you can only play audio. You are not able at this time to play video and audio with speaker groups.
I hope that answers your question! If you have any other questions or concerns for me, please let me know.
Since this thread hasn't had activity in a while, we're going to close it to keep content fresh.
We hope you were able to get the help you need from the info provided by Jeran. If you have other questions and concerns, feel free to submit another post and provide as many details as possible so that others can lend a hand.
Thanks for the help here, Jeran.