There are two things you need:
1. .ssh/known_hosts in the apache home (and .ssh directory writeable by Apache
2. .libnet-openssh-perl directory in the apache home (writeable by Apache.

For example, my Apache user is "apache" with a home directory of /var/www
I have /var/www/.ssh owned by apache, and /var/www/.libnet-openssh-perl owned by apache
I ssh to devices using my own account, then copy my known_hosts file to /var/www/.ssh/known_hosts