Oh, I meant NS record delegation (I think, terminology might be wrong, it's been a while since I futzed with low-level DNS stuff), so that you could use ns1.mydomain.com as your nameserver, even if you registered mydomain.com through namecheap.
They all allow it - just they don't all make it a simple control panel process. Either email support, or do a search and it can be taken care of on all registrars.