I don't think there is anything arong with it. I do not see how anyone can lay exclusive claim to an arrangement of plants. And although the basic design can be copied, I think it will always look somewhat different. Amano gives us basic designs to work from, he teaches it to people, whether it be the triangle, the concave, whatever... People are always inspired to copy or mimick what they see in others. That is why certain plants become so popular for a while until something else comes along.
Heres the way I see it. If you can paint the mona lisa exactly, and enter it into a contest as a replica not intending people to think its the original I dont see that as being unethical. It still took skill talent and creativity to reproduce.
If you can reproduce someone elses style so well that people cant tell the differance, I'd say you have alot of talent at aquascaping. Not just anyone can make a believable replication.
A bad copy is glaringly obvious... everyone knows bad. But good is good regardless if its your style or not.
Just playing devils advocate here, hopefully no one is offended.....