I am sorry, the update is totally broken (IMHO because redhat-release is not versioned):

[root@tux ~]# yum update epel-release
Loaded plugins: product-id, search-disabled-repos, security, subscription-manager
Setting up Update Process
Resolving Dependencies
--> Running transaction check
---> Package epel-release.noarch 0:6-8 will be updated
---> Package epel-release.noarch 0:6-9 will be an update
--> Processing Conflict: epel-release-6-9.noarch conflicts redhat-release >= 7
--> Finished Dependency Resolution
Error: epel-release conflicts with redhat-release-server-6Server-6.10.0.12.el6.x86_64
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest
[root@tux ~]# 

[root@tux ~]# rpm -qa | grep redhat-release
redhat-release-server-6Server-6.10.0.12.el6.x86_64
[root@tux ~]# 

[root@tux ~]# rpm -q --provides redhat-release-server-6Server-6.10.0.12.el6.x86_64
config(redhat-release-server) = 6Server-6.10.0.12.el6
redhat-release  
system-release  
redhat-release-server = 6Server-6.10.0.12.el6
redhat-release-server(x86-64) = 6Server-6.10.0.12.el6
[root@tux ~]# 

Please note that there is also redhat-release-workstation, thus redhat-release-server is not suitable itself as base for a requirement/conflict.