I agree with this idea! I remember way back I suggested a similar idea, so I'm glad to see someone bring it up again. One thing I suggested is that there should be a small chance that the Indominus Rex will reject the raptors, and kill them rather than act as an alpha, just to keep things interesting.
1. I repeat, the hybrids we breed in-game differ from those in the movies, a seeming hyper-aggressive natural behaviour cannot be proven. And 2. while it certainly would make things interesting, I doubt players would like it if they just spend a lot of money and time in breeding several Velociraptors just to see that they get slaughtered by another dinosaur shortly after.