I don't have a Lifeproof case, but it looks pretty standard. I can't imagine it wouldn't work.
As for other projectiles...I'm sure there are some parents out there who never let their children have toys in cars, who keep their purse in the trunk or buckled in every time, who have no drinks in the car, no umbrella, etc. But I'm not one of them. Our car has stuff, and my kids have stuff, whether it's a book, an iPad, a toy, whatever. We have umbrellas and flashlights in storage compartments in the door. I have water bottles in the cup holders. I have a box of Kleenex on the floor. My purse is usually on the floor or in the passenger seat (usually not buckled in because I forget or get lazy), etc.
Yes, those things could all become projectiles in a crash, but I'm assuming that responsibility. I think there's a big difference between an iPhone and an unsecured tool box in an open cargo area.