It also cannot evolve into Raichu and is unaffected by the Eviolite. Cosplay Pikachu is affected by the Light Ball like every other Pikachu.
-Bulbapedia
Yes, a light ball would work because Cosplay Pikachu is still a Pikachu, just special. Eviolite does not work though, since it cannot evolve, even though it is still a Pikachu.
So put a light ball on Cosplay Pikachu instead :)
Source where you can find out more.
