Active Directory DC to join another for

In our migration to AD we have encountered some difficulties. We currently have two Domain Controllers running AD.

domain.com (acting as the root)
dns1.prod.domain.com (was built before the root server)second DC

Can the (dns1.prod.domain.com) join the (domain.com) forest??

Can the (dns1.prod.domain.com) machine be a tree in the (domain.com) forest??

Or should I just uninstall/re-install AD on the DNS1.PROD.DOMAIN.COM server..??

Very confused!!
Thanks for the help.