I came across this site that has some info on how to get WordPress rewrite rules|htaccess code to work correctly on HHVM:
https://dantalion.nl/wordpress-apache-hhvm/
Many apache configurations use rewrite rules, WordPress uses them by default. To enable rewrite rules add:
RewriteRule ^(.*)\.php$ http://127.0.0.1:88/$1.php [L,P]
ProxyPassReverse / http://127.0.0.1:88/s