I think the Winter chill in Las Vegas is just enough for Lilac to bloom if planted on the north-facing side of a wall. However, the real problem is going to be in the summer with the hot desiccating air and sun beating down upon it. I would strongly suggest planting it somewhere where it will get partial shade, like under a shade tarp or wood lattice patio covering. It's definitely going to need consistent watering in the Summer and probably isn't going to thrive.