I am not nor do I know anyone pursing a DO/PHD degree. I will, however, venture to give you the small amount of knowledge how I have about DO/PhD programs.
1.) DO/PhD programs are not (to the best of my knowledge) actually considered medical scientist training programs by the NIH. The result of this is the, unline MD/PhD's, DO PhD's are not funded positions (IE the canidate gets to pay for 6-7 years of med school for a DO/PhD while MD/PhD's get a free ride)
2. There are not many DO/PhD programs. I think that the Texas, Oklahoma, and Michigan programs have them. There may be more, but not many.
3. If you want the degree to pursue academic research in the allopathic world, you're *probably* better off trying for a MD/PhD or straight PhD. DO's have made enormous strides in equality in almost ever field except bench research.
4. If you want to teach/research at a DO school, then more power to you. IMHO, DO's need more researchers at their med schools.
I *think* what I've written is correct. Some may disagree with me about the worth of a DO/PhD in an academic allopathic setting... It is possible to do, but it will be harder for a DO/PhD to chair department X at MD school Y than for an MD/Phd.
Good Luck.