There's no difference in an 'ip address' port and a ' domain name' port, they are exactly the same thing, I.e. the ip
ort. The name servers you can use from them are presumably for you to use as ns records for a domain you might buy from a domain registrar. You can then edit the dns entries for the domain at your liberty.
Alternatively, theses name servers might just be big standard name servers for your clients to use, in which case they are really nothing of interest in the slightest.