well, the sms speakers are integrated with smartthings as a thing. so apps like speaker control and big talker work easily. Alerts can interrupt the music but getting them to start playing again is hit and miss.
for voice google commands, you can only cast to google devices Natively, like chromecasts and Google homes, there are work arounds to cast to SMS but it can get involved.
also, this thread is awesome for using Google devices as speaker along side SMS. Then you can cast urls to Google devices, audio, video, tts, etc.