In the future I might need to create a script that tallies the domains on a shared IP and pings them..among other things. I was just wondering if this is possible with PHP or do I need to use shell scripting?
You can get nagios to do anything. All you need to do is write a plugin (if one doesn't already exist) to watch it and either report "OK" or "WARNING" or "CRITICAL" to standard out. You can write these scripts in PHP, Bash, C, Perl, and pretty much anything else that can, well, output a line of text to standard out.