I know this is an incredibly late reply, but incase someone else comes across it the command to summon the Domination Rex is usually | Cheat gmsummon "Indominus_character_bp_c" 1 1 0 |. Without the "|". To increase the level of the dinosaur you spawn in, you change the first 1 to a higher value. This works for any dino spawn.

thx for the command