I am not sure if Sativa bud earlier but I do that my sativa plants to begin to flower pretty quickly. As far as growing them together, I do not see an issue as I have done it. Someone else may be able to give you more info that I may not know about.
Just so you know, the sativa's will obviously get a lot taller than your indica dominant, so unless you have separate lights for both strains you will come into a problem of the light having to be way too high to give your indica's proper lighting. Hope this helps and good luck,
Elway