Splatoon will be compatible with amiibo when it launches on April 29th with its own amiibo line, and the fourth wave of Super Smash Bros. amiibo. The Inkling Boy and Inkling Girl will be available separately, and the Inkling Squid will be exclusive to the Splatoon 3-pack.
Each Splatoon amiibo will give you 20 missions, and once you finish them, they give unlock an exclusive costume.