Getting hired with an academy cert is no easier than not having one. It does show a bit of commitment though. I have a friend who instructed at one of the re-cert courses. She has had people in the classes on multiple re-certs. As far as firearms go it really depends upon the department, but I can assure you that no department is going to allow you to carry something they don't have on an approved list.
I don't want to rain on your parade but I do have to be honest, if you haven't passed the basic P.O.S.T. exam you are going to be in for a shock at the academy. They don't have time to waste on people who don't test well. It will seem like you will spend more time taking tests than anything else. You will only get a couple chances to pass each test. You don't pass you don't move on end of story. Make sure you are as prepared as you can be academically, and prepared to devote lots of free time to study, before you commit. Once you are there there are very few do overs.