Here's "proof" of Aquaman's confirmation via a tweet from Geoff Johns:

AWESOME 'cause I already played him! RT @jaroar: @geoffjohns thoughts on Aquman being in #injusticeGodsAmongUs @noobde

Also, Injustice: Gods Among Us doesn't exist because it hasn't been confirmed by the existential lords of confirmation. It is but a figment of reality, sadly.