I cannot really comment on the physics of the dogs if they are in the crate during an accident, except that I think a soft sided crate and one where you could also attach them in some way would probably be better (so they don't "slingshot" toward the front). The car seat I use (also a wheeled carrier) allows me to do this.
I would say though to please be sure you are never driving alone with the dog unsecured. I know for everyone on the board that it probably goes without saying but it really really is dangerous. A couple of years ago, my half-sister lost a very good friend because her friend was killed in in a car accident while driving with her dog loose in the front seat. She hit a bus. The newspapers speculated that the dog distracted her in some way and contributed to the accident. Obviously that is the extreme case, but it can happen and it is a horrible tragedy when it does. I'm really glad that you started this thread and are calling all of our attention to this issue.
(a.k.a. Lucky's & Sparky's mom!)