No advantage in your case. Choosing a CDN to deliver your static content was a great idea. (CDN's not only serve your content, but they cache it around their network so most locales see equivalent performance.) This offloads a significant amount of labor from your NodeJS application server.
However NGINX can be very useful in conjunction with an application server like NodeJS. Most people use NGINX as a reverse proxy, that is it sits in front of a cluster of application servers and distributes traffic load evenly.
Other cool tricks include hotswapping NGINX configuration for blue green deployments; so you never have to halt your service for an upgrade.
If you have the money and the time these are tricks well worth having up your sleeve.