I have two DCs running Server 2008 R2. Within our DNS > Forward Lookup Zones > domain.com folder we have two delegations (defaultwg & default_wg) that list our previous name servers. Because of this information I don't believe there is any reason to keep them, but I wanted to through the question out there because our domain's Pre-2000 Name is defaultwg.
Feel free to comment back with any questions.
To be honest with you this setup was before my time, so I can't comment on why those delegations were there. However, there are not forward lookup zones by those names, so I am going to be deleting them.
Thank for the help!