I figured this out.
For anyone who stumbles on the same issue, I had followed a tutorial that said to make a revive.conf file in /etc/apache2/sites-enabled/ and to set the Document Root to /var/www/html/adserver which was incorrect. I removed "adserver" from the path and restarted apache, then all was well.
That tutorial was for an older version of Revive, so I'm assuming the newest version must auto create the needed apache config files so that this step wasn't needed.