We have recently updated the IPAM service documentation to reflect a new best practice recommendation for deciding between Host Aliases and stand-alone CNAME records:
Always use a stand-alone CNAME record (instead of a Host Alias) in the case where the alias fqdn and the canonical (target) fqdn reside in different zones which are not managed by the same set of people.
For more information, see "When should I use stand-alone CNAME records?" in Stand-alone DNS Records.
