I realized that after the 1.8 update, the Indominus rex can't spook the giant herbivores/sauropods anymore, just like all the other large carnivores. You can see in this example picture I took in my experimental save.
Since the Indominus rex is the only dinosaur in the game that can kill sauropods, I think making the hybrid the only dinosaur that can scare them would not only make a little more sense since it's a sauropod killer, but also make it a little more special from all the other dinosaurs.
Since the Indominus rex is the only dinosaur in the game that can kill sauropods, I think making the hybrid the only dinosaur that can scare them would not only make a little more sense since it's a sauropod killer, but also make it a little more special from all the other dinosaurs.