check-mk-agent-1.2.6p2-1.el7.x86_64.rpm (epel7-testing-candidate) has the following requirement: "php" (which, in turn, has a bunch of other requirements). This means, that unneeded PHP software is being installed for no reason, even on hosts which have no PHP or web activity at all. My guess is that an erroneus dependency on the "php" package has been introduced to the -agent sub-package of check-mk.
The PHP dependency is there for a reason as the unitrends_* plugins do require PHP to run properly. The package is expected to include all the needed dependencies in order for it or its components to run as expected without requiring the user to install an additional package. This would be managed differently on the DEB world as there you have fields such as 'Recommends' and 'Suggests' which are handy to have especially in these specific cases. That said having the PHP package installed won't hurt or be a security issue of any kind as httpd still won't know anything about it as you would need mod_php installed.