NS records different then domains ACTUAL Name servers?

Ok, hope i dont confuse anyone.

Say you have 2 name servers, ns1.newhost.com and ns2.newhost.com.

You have a domain name, domainname.com, whose official name servers in
it's WHOIS record is ns1.oldhost.com and ns2.oldhost.com.

Say we create the EXACT same record on newhost's name servers as
exists on oldhost's name servers, including the NS records.
then, we go to the Registrar and modify that name servers to
newhosts's.

So that the whois record might look like this:

ns1.newhost.com
ns2.newhost.com

And on ns1.newhost.com and ns2.newhost.com, the DNS record looks like
this:

domainname.com. IN NS ns1.oldhost.com.
domainname.com. IN NS ns2.oldhost.com.


Now, will this work? Will the DNS request be forwarded over to the
oldhost.com's name servers, and the record grabbed from there?? A
client wants us to do this, but we've never done it before.

Question:

This is what I think you're saying:

[domainname.com registered servers]
ns1.newhost.com (127.0.0.1)
ns2.newhost.com (127.0.0.2)

[domainname.com NS records]
ns1.oldhost.com. (127.0.0.3)
ns2.oldhost.com. (127.0.0.4)

And you're asking if the oldhost.com servers will resolve all requests.

Answer:

The answer is no. If you do that then some requests will be resolved by "newhost.com" and some requests will be resolved by "oldhost.com" depending on whether the resolver wishes to use the registered name servers or the authoritative name servers in the zone.

If you tell me *why* the client is asking for *what* then I can give you a more appopriate solution.

I don't know why they want it done that way. Their 'techie' guy told them that was the best way for a 'smooth' transition. I dont understand why we can't just copy their entire record, change the NS records to ours, and have them transfer the domain name. This would be the best solution until we get their server running over here.
I'm guessing the techie doesnt completely know what he's doing.

smooth transitions are easy. All you gotta do is setup the new dns server with the domain with the same exact information as the original dns server except the NS records are different. Then, change the registered hosts for the domain. For a few days after the registry updates make sure both old and new hosts stay online so that any cached information is purged and everybody is using the new server. Then you remove the domain from the old server.