Atomicorp

I have a server with Red Hat Ent. Linux AS release 3 (Taroon Update 1)

I had been using ARTs 3ES repos, but they're gone...

What should I use now?

Is using: http://mirror.centos.org/centos/3
...or: http://mirror.centos.org/centos/3.8
alright to use?

or do I need to use a Redhat repo?

Use http://mirror.centos.org/centos/3/, thats a symlink to 3.8. They will change that symlink to point to each new point release upgrade they do automatically. It's not entirely a bad thing to mix the centos and redhat update sources on the same box, although if you're paying for the redhat subscription you should probably stick with it. Just keep in mind eventually you'll get a centos update that is going to break up2date's integration with the red hat archive.