I'm afraid you cannot disable a database connect function from apache configuration. It can be done from php.ini and in this case it's global.
The only thing that comes in mind, is to disable php for server2 using
php_flag engine off
in a .htaccess in the docroot of server2, or inside the vhost2 definition in httpd.conf.
Of course this will stop parsing all php pages and will break vhost2 if it's written in php.