Yes you can find a job with this degree, and yes it can help you get into med school if your gpa is significantly better. There are other masters programs out there that guarantee you acceptance to their med school if you maintain a certain gpa. You'll have to look for those though. Otherwise consider D.O. schools. I'm still wary of the Caribbean schools though....just a personal thing. Good luck
I don't think that just doing an MPH degree and then getting a job with it with a 2.7 undergrad GPA will be too much help. You need to show med schools that you can do well in science classes, not MPH classes. If you're graduating with 2.7 GPA (or even around 3.1-3.3), I think you need to raise the GPA with upper level science classes...that is, complete a Post-Bac Program or get a GMS degree (several schools over it, such as BU). Overall, with 2.7, it'll be hard getting into any medical school, be it allopathic or D.O.
Public health is a great field, but having an MPH doesn't really make up for a low GPA, especially if you're struggling in the sciences. You might try the SDN postbacc forum (http://forums.studentdoctor.net/forumdisplay.php?f=71) to learn more about the master's programs that can compensate for a low GPA to boost your med school app. I guess first you need to decide which direction you want your career planning to go. Good luck!
From what I remember from my days as a premed reading through the SDN pre-allo forums, graduate degree courses don't count towards your undergrad GPA calculation, which is perhaps one of the biggest factors considered during the admissions process. I would suggest going to the pre-allo forums for more info (http://forums.studentdoctor.net/forumdisplay.php?f=10).