Why not - they are the same old mirrors - all that happens is that yum gets a lost of local up to date mirrors for the release/repo/arch from the mirrorlist server on port 81 - chosen solely so that we can run it on the same server as normal apache on port 80.
If you have fastestmirror plugin enabld yum will then test the mirrors and use the fastest local connection.
The version of yumex that we have at dev.centos.org alsouses the same mirrorlist system.
Note that using a non-standard port (81) here is an error - many restrictive firewalls (or proxies) won't allow such a connection - for example at my Mom's work (were I'm now) and my Dad's. Even though it's an outgoing connection.
Setup apache virtual hosting, add a new dns name, and use apache's proxy module to proxy mirrorlister:80 to localhost:81 otherwise this will break for a lot of people.
Cheers, MaZe.