The activation service needs a vendor label to activate a service tag. rhn504 always sends 'REDHAT' as this label (for installation numbers), when it should be sending 'DELL'.
This is in relation to the dell service tag cron job that we use to obtain dell service tags and their associated entitlements from dell. This is an issue for customers that purchase a dell computer with a RHEL5 entitlement, and then try to activate using their service tag with rhn_register. The directions we send them tell them to activate via the web interface, but this process should also work. To trick RHN register into using a dell service tag on our regular machine, we followed the steps here: https://wwwapps.rdu.redhat.com/w3xwiki/index.php/Rhn_Register_Instructions Customers will not experience any problems as long as they use the web application for activation.
If you need to test a dell service tag, the easiest way to add one is to use the Hock application to hock a service tag. This can be selected from the main menu of hock. You can check in the table web_dell_service_tags_shipped for info about the service tag you create. You can also activate these with the dell activate web application.