Sao has no server so you need a web server to serve it.
You can use another web server than the Tryton’s builtin but then sao will post requests to this one. So this external server must forward (reverse-proxy) the request to the trytond server.
But frankly there are no much advantage for such architecture. Indeed a most common usage is to put a web server (like nginx) in front of trytond (werkzeug or µwsgi). This allow to support http2 connection or gzip compression for example.
Indeed with the current docker images there is no need to take care about what is updated. You just recreate the image and everything (server, sao, modules) is updated.