For those that want to know if you can add a single DNS host entry that points to another domain, you can. First, you will need to create and add a new zone into your DNS server. The new zone will need to be the full domain address of the host entry that you want to point to.
For example, if you want to add an entry that point to ftp.domain2.com from domain1.com, you will need to create a new zone named “ftp.domain2.com”. After the new zone is created, you then need to create a host entry in it. You will need to leave the “Name” section blank and enter the host IP address for ftp.domain2.com.
You should now be able to ping the new dns entry by DNS.