Foreman currently only enforces unique names via Rails validator:

https://github.com/theforeman/foreman/blob/develop/app/models/host/base.rb#L39

There are some cases in concurrent environments where two hosts can be created with the same name. This should be prevented on the database level using a constraint.

Discussion:

https://community.theforeman.org/t/why-dont-we-have-unique-index-on-host-names/24071