Honestly, it's hard to say...
I got into two of the best DO schools without research (PCOM & CCOM).
That said, I have a bunch of clinical experience... in group practices and in hospitals --
My personal opinion on the *general* hierarchy of emphasis would be placed in the following order:
1. science GPA
2. cumulative GPA
3. MCAT
4. Letters of Recommendation
5. Clinical experience
6a. Research
6b. Teaching (MCAT prep, intro courses, etc)
7a. Other extracurriculars (sports, etc)
7b. non-medical community involvement
With few exceptions, there are a large quantity of things that are higher up on their priority list than research... so if you want to do or have done research, that is a great addition to an already-strong application. Preference would probably be given to being credited on a published, peer-reviewed paper... the larger the role, the better.
There is no doubt in my mind that MCAT, GPA, and LORs are chief concerns of admissions committees...
Please remember that I am not on an adcomm though...