gpa accounts for somewhere around 25% of the mcat score variance (r=~0.5). This makes it a respectable correlate but nowhere close to a definite prediction. It's probably akin to looking at the sky and seeing clouds and saying it'll probably thunder and lightning today. In reality, we could have a thunder storm w/o visible clouds and visible clouds definitely don't tell us we will have a storm, but it does make it more likely. Additionally, because of the difficulty of the mcat, i don't think it's ever really appropriate to imply that "if you just get a 32+ on the mcat, that'll make up for your grades" when, in reality, most students that did well in school and understood the topics probably won't break 32. It's simply not realistic. Does it happen? Sure, but it's too rare to tell someone to rely upon it happening.
Likewise, it is absolutely possible to get in with a 3.0/25. These students are usually non-trads with terrible grades from 10 yrs ago who aced every prereq and had other stunning qualities. Truthfully, a few people get in with almost any gpa and mcat. The reality, however, is that the numbers quickly trend downward once we get below about 3.6/30. (the evidence here lies in the fact that the average accepted student has a 3.66/32, while the average applicant has a 3.4/28 and does not get in, since only about the top 40% of applicants are accepted anywhere.)