Yes you can! Nginx is a reverse proxy, so you can configure one location block to try netlify and one to try your ghost instance! Here’s a snippet from what I use:
location / {
try_files $uri $uri/ @netlify;
}
location /blog {
# Include Ghost config here!
}
location @netlify {
proxy_pass https://<SITENAME>.netlify.com;
include /etc/nginx/proxy_params;
}