Why have rate limiting at all? Just disable it

Maybe they don't have an unlimited budget for bandwidth charges? I'd strongly recommend they go behind a (free or cheap) caching CDN first before removing limits.

Also, the rate limiting is probably meant to be based upon the client's IP, not the proxy IP. Usually, the proxy adds the client IPs to the request headers and you can use those in Nginx rules.

Seems like the host is down altogether for me.

For me too.

Host pings, but port 80 is dead.