Its gonna be really annoying if you have to prep your pokemon before a battle to ensure it gets max crit ratio and evasion and all that. Wont be so sad if you can raise it and it doest drop, but seeing as their is a hunger stat it seems unlikely.
I imagine you won't be forced into it beyond the tutorial. Will people who use it get some buffs from it? Probably. But I bet all Pokemon Amie bonuses are canceled out for online battles, only being applicable against in-game trainers. So you're probably not at a loss if you don't want to use it.