False. They don't even need to add it to their profile. The NIP-05 is valid regardless, as long as the entry exists with their pubkey. One user can have many valid NIP-05s whilst only adding one or none to their profile
Discussion
Are you sure that all applies to ditto? Same app that thought a persistent notification dot begging me to add NIP-05 to my profile wasn't enough so they added a banner that straight-up lies and says I don't have a username, while my username shows up in the same app and there are multiple valid NIP-05 entries for it out there just not on my profile