In case this is of any use to anyone, I was able to add a Sutton InComm Vanilla physical gift card (said Happy Birthday on it) from Walmart to google wallet and use it to pay my Progressive insurance bill in the app.

It failed to add to tap-to-pay (disappointing since my last virtual Vanilla worked fine), but it still worked for paying in the app.

The reason I care is that I just want to have a fallback in case my other gift card liquidation methods don't work.