It is totally fine to post both places. When you are a pre-med you may not know where you want to apply. Most of the information you gain from both forums is applicable to either DO or MD students.
Over the last 4 years I have posted on both places, although I will admit I have posted more in the pre-allo, than I have in the pre-DO. When I was an undergrad I wasn't sure where I wanted to go to school. Even though I didn't post much in pre-DO, I did read all the posts.