[McMelchior]

"Ethics" must be based on a foundation of ideology. Like from the Nazi's point of view nothing they did was un-ethical, since their (atrocious) acts were based in their ideology (absolutely no comparison, just an illustration).

Back to tournament poker, if the foundation is that "Thou shall not do anything that puts other players at unfair (that is, not skill-related) disadvantage" both descibed scenarios are un-ethical.

Since anybody can (and in the long run eventually will) experience force majeure preventing them from finishing a tournament, but not all players have access to a qualified stand-in, an unfair advantage is gained.

Anyway, since most sites TOS explicitly prohibits stand-ins, and TOS must be considered part of the rules of the game (even for all) breaking them is un-ethical in itself.