debian-policy states required targets, is dh pass ok?

https://www.debian.org/doc/debian-policy/ch-source.html#main-building-script-debian-rules

Document in question ^

I am learning to build debian packages and read above policy, specifically about the main (required) targets.

• I was told that I don't need to specify the targets if I use dh. Is this valid to the policy that dh delivers these targets?

.. of course one will have to override where the dh commands fail to do a proper job.

• Is there any case where you absolutely need to manually define targets for compatibility, or would it be rejected solely for missing the targets explicitly defined?

No, the required targets do not need to be specified explicitly in debian/rules. The policy only requires that debian/rules "implements" those targets; that is, if you call debian/rules with any of those targets, it should do the appropriate thing.

There are many packages in the archive now which use dh and which don't declare those required targets explicitly in the debian/rules makefile.