Zeritz-
Welcome to the message boards. You are not too late by sending in your application in September (I'm assuming you mean your primary; if you're talking about the secondary then you are right on top of things/early). After receiving the primary, they will send you a secondary within a couple of weeks, which you should try and get done as soon as possible. Then, make sure your file is complete (letters of rec, etc) also, because they won't review your file until everything is in. I saved copies of everything I sent, and called several times to verify everything had been received. It would suck if something got lost in the mail, you never knew about it, and the school never told you. So verify everything.
The general consensus that I heard and thought myself was that CCOM was one of the easier interviews. The interview day is basically structured in such a way that you get a brief introduction/welcome, a tour around campus, about a 30 minute interview, and then a financial aid presentation and lunch. You're typically there from around 8-1pm. For my interview, there were 3 people (a DO, a PhD, and an MS-4). It was pretty laid back, without a bunch of pre-formulated questions. I pretty much just started talking, and they asked questions as we went along to get to know me better. It was pretty low stress.
I am unaware as to how strict they are about the D.O. letter of recommendation. I sent one in, but I don't know if it was required or not. You may want to check with the admission office on that one. As far as finding a D.O., most areas do have them, but you may have to look harder. One way to search may be by contacting MDs you know, chances are they will know a D.O. or two that you can meet up with. Don't be too picky about the specialty. This is something you should do ASAP in order to have your file completed.
Other recommendations...when you call to talk to people in the admissions office, ask to speak with an admissions counselor (not the lady who first picks up the phone). They tend to be much more helpful and direct, as they have access to statistics and more timely information. Also, sending in extra letters of recommendation, updates to your file, etc. are a very good idea. This shows continued interest and is looked upon favorably.
Anyway, hope I could help. Let me know when you get that interview!