Well, actually no it is not.
The nameservers run on a set of “tables” consisting of multiple records of various types. That is pretty easy. However, when you look at the nameserver, say the granddaddy of UNIX nameservers called “bind”, and its tables you can tell that the names in the tables are relative to the domain. There is a file for each domain and everything about that domain is in that file.
The problem is that you can put a CNAME (or Cannoical Name, aka “alias”) record into the tables. It is legal to say that “www.host.com” is the same as “host.com” or “ftp.host.com” is the same as “ssh.host.com” which is the same as “host.com” and “www.host.com”.
It is NOT legal to say “www.host.com” is the same as “www.barbq.com” because “host.com” is not in the same domain as “barbq.com”. You can’t put a name into “host.com”'s table for the “barbq.com” domain.
That is where the redirect comes into play. The redirect is really something that the web server gives the web browser when it wants a page. Say that your page reference is to www.host.com and you want the “index.html” page. Well, you tell the web server on www.host.com that the index.html page is to be redirected to www.barbq.com’s index.html page. That is legal. It is legal because what goes back to the web browser is an error code that you have either temporarily or permanetly moved the web page “index.html” from www.host.com to www.barbq.com. The web browser will then re-request the page from www.barbq.com.
A temporary relocation does not change the page reference. It would still say that the page is located at www.host.com.
A permanent relocation will change the page reference on the browser line.
But, in no case can you put into either host.com nor barbq.com nameserver tables a cross-domain reference and have it work because all of the domain references in the table are relative to the one domain that is being described.
This does not apply to service references such as the MX records. Those point to whole names; but you did not ask about email servers.