ISPConfig runs on its own version of Apache and PHP. The "supports PHP 5.2" feature in the new version of ISPConfig is really saying that the version of PHP ISPConfig installs for its own use is 5.2, correct? That version does not affect anything else I do.
Yes, you need either PHP 5.2 from Fedora or you will have to recompile it. It might be better to use a version from Fedora if possible, But'Iam not so familar with extended YUM options to help you on this issue.