Google Voice SMS messages not showing up in Hangouts
I was having this problem too. But I went to Settings > Apps > Messaging and disabled the stock messenger app. Then everything goes through hangouts. But I ended up just going back to the old Google Voice app bc I couldn't get my phone calls to work right with Hangouts. It wasn't forwarding right, so I missed calls, and it wouldn't use my Google Voice voicemail system (it kept using my stock VM system). If you have any help with these, please let me know.