I'm currently working on a similar problem. I don't have nearly as many servers to update, but they aren't connected directly to the internet. I just installed yum (needed like 4 dependencies) and createrepo using the rpm command. You can get them from http://dag.wieers.com/rpm/packages/
. Then i used createrepo to make the repository, and edited yum.conf to point to the directory where the repo was created. I believe the line is baseurl=file:///path/to/dir whee dir contains the 'repodata' folder that was created by createrepo. Then all you have to do is run 'yum update'.
edit: I did this to upgrade from 4.3 to 4.8 and didn't get any problems. I updated all the packages and then ran 'yum install kernel' after, and modified grub.conf to point to it (yum won't do this automatically). Everything seems to have gone fine..