There are many examples where you may need to have a specific subdomain's DNS be managed by a different nameserver. cPanel makes this very easy.
Log into WHM.
Click on DNS Functions, then Edit DNS Zone.
Choose the domain that you want to create the subdomain for.
Once you are in the screen, scroll to the bottom.
Enter in the subdomain and select NS as the type of record. For the hostname, put in the nameserver's hostname followed by a .
Hit save at the bottom and the new record will be in place.