Does FileMaker Server 16 prevent use of the system apache in macOS?

I'm running FileMaker Server 16 ("FMS") on macOS High Sierra, *without* the macOS Server package. I set the FMS web server components up on ports 8080 and 8443 because I wanted to continue running other web services on ports 80 and 443. I notice that FMS runs /usr/sbin/httpd (i.e. Apache) under its fmserver user, with configuration at /Library/FileMaker Server/HTTPServer/conf/httpd.conf. I was trying to configure the system Apache (at /etc/apache2/httpd.conf and using apachectl start), but couldn't get it working at all, even with the default config. apachectl -t said Syntax OK. There were no error messages or logs, and connections to port 80 were refused. The only relevant thing I could find on the web is [a report of the FMS installer refusing to install if Apache is running as part of macOS Server](http://automatica.com.au/2017/07/install-filemaker-server-16-on-a-mac-with-macos-server-app-v5/) . I was able to serve on port 80 using nginx installed via brew. Is the fact that FMS is running apache preventing me from running it under another user?