I wouldn't use it. Use the right tool for the right job.

Nginx is good at caching but Varnish is often better.

HAProxy is far better suited to providing load-balanced HA. Regarding this article, this API makes is ideal to dynamically-reconfigure HAproxy, adding and removing servers on-the-fly, which is super-useful in production.

Only at the most minimal layer, meant for favicon.ico requests and the like. They are explicit about not becoming a cache or web server.