What is the best practice for Nginx/ELB/Unicorn architecture on AWS?

We have an RoR application in AWS Beijing. AWS Beijing does not have Route 53 (We can't use Alias to apply ELB to Apex domain), so we must use a Front-end Server running Nginx in front of ELB.

Now our architecture likes below:

Front-end (Nginx) -- ELB --- App-(1~n) (Nginx--Unicorn)

We have noticed the words from Unicorn description below: "Unicorn must never be exposed to slow clients, as it will never ever use new-fangled things like non-blocking socket I/O, threads, epoll or kqueue. Unicorn must be used with a fully-buffering reverse proxy such as nginx for slow clients."

So my question are:
1. Before Unicorn, do we need nginx on the App Server?
2. If we remove nginx on App Server, can nginx on Front-end Server play such the effect like unicorn describing?