This repo has made efforts not to replace system packages. In some cases it has endeavored to directly address CentOS compatibility but has expressly denied inter-repository compatability as a goal. It may not mix well with other 3rd party repos. So, make SURE you are using the Priorities yum plugin if you are using EPEL ... especially if you mix its packages with those from other 3rd party repos. It should also be noted that, while EPEL may not overwrite distro packages, it may have conflicts with the CentOS extras repo which is enabled by default.