Again, like I said before, if you can find a DO or MD medical school to sponsor you, then you can take the USMLE. I would assume that dental schools who have basic science courses with their perspective medical schools, their chances can be higher. I know here at NSU, since we have a DO medical school, the chance of taking the USMLE can be there also. A lot of loops and barriers, a student will have to jump through, but it can be possible (don't quote me on this).
DO medical students take the COMLEX instead of USMLE, but many of the DO students register for the USMLE to increase their residency matching process.