When the nuts is actually on board, like T♠J♥Q⋄K♣A♠, I would say it's probably bad etiquette to continue raising in a cash game where the rake will be affected accordingly (although I have in the past seen people fold on the river in situations like this, albeit infrequently, but it happened!).
In a tournament (where rake is not a consideration), it's only likely to be a small handful of raises until you're all-in anyway, so unless someone is taking an age to make each raise, I don't see that there's any significant detriment or inconvenience caused, so I wouldn't consider this bad etiquette either.
While most games are governed by rules which include one to penalise players for not raising on the river with the nuts (to prevent soft-playing), I've never seen this enforced when the nuts is on board and would expect Rule #1 to take effect (i.e. common sense or an unusual situation can permit a floor to make a decision contrary to the rest of the rules).
However, when it is possible that it's not a split pot, I think anyone is well within their rights to raise as many times as they would like. If you have
Ax on a
22223 board, why should you give up potential value against someone playing
Kx who might be willing to get all-in?
All that said, what is and isn't good etiquette is basically a matter of (mass) opinion, so one person's view is not necessarily particularly relevant - it matters what "most" poker players think. If enough players started changing their mind and felt that some particular behaviour was unacceptable, it would become bad etiquette where it might not have been previously.