As others have said, someone will eventually ask you what you are doing with your application year. If you omit the fact that you are a DO student, you are being dishonest, and you will tank your application rapidly. Some people may argue that you could lie and get away with it. I think differently:
-If you apply for MD programs, I imagine that you will be using many of the same LOR writers as you used for the DO programs. I wouldn't be surprised if some mention of DO school made its way into one of those letters.
-What if you are offered interview dates that you absolutely cannot make because of time commitments at the DO school? How do you plan to explain why you need an alternate date? (Note, some MD programs are flexible with this, others are not).
-Sometimes, interviewers or student hosts will google candidates before they arrive. What if a site listing you as a member of the "class of XXXX" at your school pops up?
Maybe none of these situations will apply to you, but you never know when your interviewer will know someone at your current school, or when you might slip up with what you say. I am absolutely not advocating lying about your current status - I am just providing a few examples of how even the best liar could be caught.
If you are just honest from the start, your chances aren't much better. Some interviewers will be of the mindset that MD>DO, but I think almost all will agree that a DO school should never be used as a placeholder for an MD school. When you take a seat at one school that you do not want, you keep someone else from getting in who probably wanted it desperately. If you only want MD, then only apply MD.