I'm not sure I even understand the basis of the question. To me, the answer is intuitive. To obtain an allopathic/osteopathic residency in a medical specialty, you must have a medical or osteopathic degree.
As MaxillofacialMN corrected stated, I don't think you'll be finding any cardiothoracic surgeons who are DPM's, no neurosurgeons who are DPM's, no ENT docs who are DPM's, no gastroenterologists who are DPM's, etc.
Pathology is a residency offered to MD/DO graduates. Similarly, I'm not aware of any MD/DO graduates who have obtained a podiatric surgical residency.