Try
yum list installed | grep reponame
On one of my servers:
yum list installed | grep remi ImageMagick2.x86_64 6.6.5.10-1.el5.remi installed memcache.x86_64 1.4.5-2.el5.remi installed mysql.x86_64 5.1.54-1.el5.remi installed mysql-devel.x86_64 5.1.54-1.el5.remi installed mysql-libs.x86_64 5.1.54-1.el5.remi installed mysql-server.x86_64 5.1.54-1.el5.remi installed mysqlclient15.x86_64 5.0.67-1.el5.remi installed php.x86_64 5.3.5-1.el5.remi installed php-cli.x86_64 5.3.5-1.el5.remi installed php-common.x86_64 5.3.5-1.el5.remi installed php-domxml-php4-php5.noarch 1.21.2-1.el5.remi installed php-fpm.x86_64 5.3.5-1.el5.remi installed php-gd.x86_64 5.3.5-1.el5.remi installed php-mbstring.x86_64 5.3.5-1.el5.remi installed php-mcrypt.x86_64 5.3.5-1.el5.remi installed php-mysql.x86_64 5.3.5-1.el5.remi installed php-pdo.x86_64 5.3.5-1.el5.remi installed php-pear.noarch 1:1.9.1-6.el5.remi installed php-pecl-apc.x86_64 3.1.6-1.el5.remi installed php-pecl-imagick.x86_64 3.0.1-1.el5.remi.1 installed php-pecl-memcache.x86_64 3.0.5-1.el5.remi installed php-pecl-xdebug.x86_64 2.1.0-1.el5.remi installed php-soap.x86_64 5.3.5-1.el5.remi installed php-xml.x86_64 5.3.5-1.el5.remi installed remi-release.noarch 5-8.el5.remi installed
It works.