Atsushi Umebori, Slavomir Kowalewski & Kenji Iwata are listed in the booklet under assistance (協力). On Kenji Iwata's website he says he arranged the main theme and other tracks:
http://www.iwatakenji.com/#works
I've seen many times where an assistant credits themselves as an arranger on their website, yet only receive a copyist/special thanks/production credit in the booklet.
What do you think we should do in these cases?
EDIT: If no one has any opinion on it, then I'm adding as arrangers.