I didn't get my application submitted until August 15th. I KNOW that I lost some interviews because of it. I still got other pre-Dec interviews and I was still accepted to multiple schools, but I had less options and added stress because of it. It really ended up costing me even more money as I had to make a deposit on a Dec 1 acceptance, just to get a January interview at another school that I'll be attending. An interview that I would have gotten early had my application been in.
You just need to be honest with your stats, your experience, and the overall strength of your application. With decent stats and ECs, you'll still get in, but you'll need to apply to more schools and you'll end up with fewer interviews and options. With lower or even an average application, you may want to wait, especially since you won't know your DAT scores going in.
If your GPA is strong and ECs are awesome, then I think having fewer options is better than waiting a year.