I was hired into the immersion program as a new grad, and I did not work at Regions prior (as a PCA or anything). Although its tempting to want to start out right in ICU, I found the program's format to be very good. I started on a telemetry cardiac progressive care unit. Like I said, the classes and orientation as a whole is outstanding. When our census is low, we do have to float to other ICUs or the progressive/general care floors, so I have been to several.
It seems like most of the immersion program RNs were new grads--so not limited to internal applicants.
I'm sorry I can't give much advice on how to increase your odds of getting hired--I'm not sure what exactly they look for--I did not have a nursing internship before, was not a PCA. I had a supervisory position at the job I had throughout college. My cummulative GPA was 3.92, I was in several honor societies, had letters of recommendation from 2 of my professors & I did take a critical care class as an elective my senior year.
Hope that helps, good luck!!