You can host both on the same machine but using two different services, the static content could be served from nginx directly, but the shiny app has to be served necessarily from shiny-server, since both are on the same machine, you could define a path to the shiny app or an http address pointing to the port 3838 in your iframe
<iframe src="/srv/shiny-server/sample-apps/hello/" style="border: 1px solid #AAA; width: 290px; height: 460px"></iframe>