Yes, you can generally think of it as a replacement for mod_php as Unit would parse requests from NGINX, pass them along to the PHP parser, then return the responses back to NGINX. That's the same job mod_php does for Apache and what PHP-FPM (essentially) does for servers like NGINX.
You can see the PHP configuration here:
http://unit.nginx.org/docs-configuration.html#php-applicatio...
And here's the configuration needed to integrate Unit with NGINX:
http://unit.nginx.org/docs-integration-with-nginx.html