I have found documentation on the web which states the following:
"Enabling FastCGI for all PHP switches your site over to using mod_fcgid"
There is an checkbox option in the Dreamhost PS configuration page which states:
Removes mod_php from the Apache web server. This will save a significant amount of memory if your site serves a lot of static :content. PHP-intensive sites may benefit more from setting all domains to use mod_php in Manage Domains and enabling a PHP cache"
So could I do disable mod_php if all my sites are configured as Fast CGI without an issue to save a bit on the memory? My websites are all wordpress sites. Xcache is of course enabled as well.