Yes you are right, php_mod can use only one version, if we want more versions, fpm is the way -> http://blog.remirepo.net/post/2013/11/07/Various-PHP-versions-on-an-Apache-server but it requires to change a lot in apache and thus a stock nethserver.
With nethserver-php-scl I use CGI when I want to use a specific version of PHP for a shared folder, but performances can be lower, however all is reversible, no huge changes needed.
With the same rpm I did for SME Server, I know that a lot of people use the webapp owncloud8 as is with the software collection in an Ibay, but of course if the same is done here, all your ldap integration will be lost and should be made manually in the webapp.