Giving a the most flimsy reason for the policy doesn't give me confidence in that; I can think of much better reasons for disallowing uid aliases (root or otherwise).

It has the same optics as an unauthorized entry someone planted: a backdoor to retain root access. It will continuously have to be explained to new people who spot it.

If the intent is to keep the passwords identical (which it probably should be), the tooling doesn't support it. When someone changes the password for root using standard tools, the one for rotorooter doesn't sync. This is a problem if someone is changing the password in order to restrict access to just a specific set of people who know the new password. The unaltered entry turns into a de facto backdoor for everyone knowing the old password.

Pitafall: if you put an alias entry in the wrong spot in in the password file, so that it appears before the canonical entry, then UID 0 maps backward to the alias name (e.g. via the getpwuid() function). This breaks all logic that looks for the string "root" rather than UID 0. E.g. shell scripts looking for root in the output of some command.

I’m confused; Your entire response seems like reasons to not do this.