This is a tricky question, and the answer is yes and no. In Netflix’s terms and conditions, it states: “You may view Netflix content primarily within the country in which you have established your account and only in geographic locations where we offer our service and have licensed such content.”
So if you live in the US and connect to a VPN’s US server to watch Netflix, you are within the boundaries of the streaming service’s terms and conditions. However, if you’re traveling outside of the country where you have registered your Netflix account, it seems that you’d be allowed to use a VPN to access content available in the country where your account is registered. Netflix also says you can watch in-country content (i.e. if you registered your Netflix account in the US and travel to Germany, you can access US + German Netflix).
Some VPNs are better than others at accessing Netflix (and many other popular streaming sites). Most of my top VPNs are excellent for streaming — ExpressVPN, Private Internet Access, and CyberGhost VPN all provided me with fast and uninterrupted streaming on Netflix, Hulu, and Amazon Prime during my tests.