Can you evolve Feebas by trading with Prism Scale on RSE and DPP?

Question

Because both games have Pokémon Contest.

Answer 1

It evolves from Feebas when leveled up with its Beautiful condition high enough, or (from Generation V onward) when traded holding a Prism Scale.

So, no. Since RSE is in Gen 3, which is before Gen 5, you must evolve it by raising its Beautiful condition and then leveling up. Additionally, Prism Scale wasn't introduced until Gen 5.
Source: https://bulbapedia.bulbagarden.net/wiki/Milotic_(Pokémon)

Comments

So how do you evolve it in HeartGold and SoulSilver?

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You can get the haircut brothers or Daisy to groom your Feebas. https://bulbapedia.bulbagarden.net/wiki/Beautiful_(condition)

Answer 2

The Prism Scale (Japanese: きれいなウロコ Beautiful Scale) is a type of held item introduced in Generation V.

source
Prism scales don't exist in RSE and DPPt. so no