How is this configured? I've never seen an incoming call shown as possible spam.
In fact, when I tell Google Voice a number is spam, while it won't forward calls from that number anymore, it still forwards both calls and texts to Hangouts. The only way to prevent Hangouts from receiving known spam is to block the number, which is buried in the app. (I hate Hangouts, it has to be the best self-torture app ever.)
Edit: As I was typing this, I received notification on both my phone (Hangouts) and in my web browser (Hangouts) of a voicemail from a number previously marked as spam. "Our system is showing your local Google listing is currently not managed or has not been properly cleaned and verified ..." In Google Voice, this voicemail is in the Spam folder. And yet I received two notifications on my devices for it.