With the exception of Special Masters Programs such as Georgetown, taking med school courses might not work any better than more undergraduate/graduate coursework. Thats assuming you can even take med school courses in a non-degree earning program.
Georgetown's SMP is well known thats why it works. However if you take med school courses through a less known program, most schools may even think the class is a grad school course. Med school coursework is still graduate level, and thus would count on your grad GPA, NOT post-bacc, regardless of the program.
The other factor is, taking a few med school courses does not fully show your capacity to do well in med school. You are taking a select group of courses, not doing the whole curriculum. Essentially if you took 1-2 med school courses a semester/quarter, and get A's, although this is a good thing, it still doesn't say you can handle a full med school semester/quarter where they take more than 2 classes. Lastly, since most people apply with only undergrad grades, undergrad coursework is emphasized over grad/med work.
For my PhD program, I am required to take our med school's general pathology, systemic pathology, and medical statistics course. With the option of taking the year long pharmacology/toxicology series. Despite all that, our med school's director of admissions says that I should still take undergrad courses if my program allows it (which it does) in order to improve my application. This is why advisors emphasize doing post-bacc and take ONLY undergrad upper division coursework. They usually discourage doing a masters/PhD since some programs do not let their students (or students do not have time) take undergrad classes as electives.
Pretty much, it won't hurt you to take those classes, but don't put too much stake into those classes being a quick way to get admitted into a med school. If thats the case, I wouldn't be planning to take undergrad classes while finishing my thesis over the next 2-3 years, even though I will finish my core grad curriculum this quarter.