I went the business school route to professional school so that I'd have more options if I changed my mind or didn't get in. It is very easy to keep a high GPA in the business school. If you attend class for every lecture you can usually get an A with minimal studying. I can't speak for medical applicants, but for dental the prereqs that you take will do a good job of preparing you for the DAT, so if you work hard studying for the DAT you'll have a high GPA and a high DAT score that will make it easy to get into dental school.
The only negative, which can be pretty huge, is that it doesn't prepare you for dental/medical school like BIMS and other tough majors do. I was used to cramming for 2 hours before a test and making a 95+ for most of my college classes outside of organic chemistry. When I started dental school I honestly didn't know how to study for the types of tests that you regularly take there. You are required to memorize large amounts of material and it's not the kind of stuff that you can prepare for in 2 hours or even a weekend in some classes. I felt that my classmates with a background in BIMS or similar majors were used to these types of tests and more prepared to study for them when we started out. Also, I managed to make it there without ever taking anatomy, biochemistry, microbiology, or histology and many of my classmates had two or more semesters in these subjects when they started school. That experience also had them more prepared for those classes.
If I was advising someone on what to do, I'd say that if you are 100% sure that you want to go to professional school and you are 100% sure that you have what it takes to have a great GPA as a BIMS major, you should go that route. It will give the best chance for continued success in professional school so you can finish at the top of your class there.
If you're not 100% sure about the whole professional school thing, pick a major that you'll perform well in (like business) and take the prereqs on top of that. If you go this route, make sure that you get guidance from someone that has chosen a similar path to professional school so that you will be prepared for the huge jump in the level of difficulty from the easy major to professional school. If you're smart enough you'll adapt and be happy you chose that route, but you are better off adapting before you start school than dropping two Fs on your first two major tests because you thought you could still get away with cramming.