While Perry himself won't be joining since he wants to go through it to prove to Joker that he's fearless, he does have Pokemon who would want to join! Namely his Phantump, Galvantula, and Pangoro, because nothing's scarier than a shy ghost, an overexcited spider, and a giant panda who won't stop bragging about everything.

Because of that Perry might join rehearsals to make sure everything is going alright. (and so no one accidentally scares his Phantump to the point of crying)