There will be exceptions in both directions (people with higher GPA who didn't get in, people with lower who did). I don't think getting an 'A' in 4 courses would in most adcoms eyes wipe the academic slate clean however. Infact some schools even stipulate a minimum number of credit hours before they will even consider the work as a separate 'postbac' GPA rather than lumping it in with undergrad work.
Most regular postbac courses are 1-2 years of full-course load. I think you should aim to accomplish outstanding grades on that kind of course-committment level before you can feel confident schools will look at it as significant and look past a sub 3.0 UG GPA.
As with all advice on here - this is just my opinion, and I don't sit on an adcom.