You don't need to do an extra 1-2 years, you can get an MD license after the first year of residency. This route would be 4 years of DS, 4 years of MS, and 4 years of OMFS = 12 years. Another way to achieve equivalent degrees (DDS and MD) would be 4 years of DS + 6 years OMFS residency = 10 years at best. This is assuming you get in right after dental school and don't have to do gprs/internships. That is easier said than done. At most you would be adding 2 years, not 5. Many OMFS programs charge you tuition for the 2 years of medical school, so you would be doing an additional 2 years of medical school. Considering the range of tuition/debt people have just coming out of dental school, it's not that big of a deal. I went to a cheap state school and have less than $150,000 in debt, but I have friends that graduated from NYU and have closer to $400,000 of debt. Nobody would say, "I want to use medical specialties as a fallback" in an interview, it's merely a pro for this route. It offers a decent Plan B, something that a couple years of unaccredited internships does not.
To say Oral and Maxillofacial Surgeons specifically are not physicians is a bit much. Many go to both dental and medical school, spend many years in a hospital, treat arthritic joints, fractures, cleft lip and palate, etc. Is a psychiatrist a physician? If they are, OMFS certainly are. If not, I guess they shouldn't let those people in either since they aren't going to be physicians. Applying to both medical and dental school at the same time is not the same thing at all. There is a huge difference between someone who successfully completes a professional program and makes a calculated decision to further their education and an undergrad who throws applications in for both because they're unsure and heard one might make more money.
There is a lot of synergy with medicine and dentistry - they are not mutually exclusive. It's not like being an astronaut and then deciding to go to med school - that might show lack of committment to a profession. You can't claim to be committed to dentistry and throw medicine out the window. A DDS and MD is not an unheard of combination of degrees. There is a lot of overlap in these fields, and it puts you in an ideal position to pursue a subspecialty like head and neck or a craniofacial fellowship. A dual degree passionate surgeon with a sincere interest would be an strong asset to participate in research, develop new procedures, etc. in these fields. I'm pretty sure the admissions committees are well aware of that.