I have been replacing iPod Touch 4th gen digitizers for a while now. and yes, i have run into the same issue in that about 3 out of 10 of the cameras don't work. I haven't found a way to fix the camera issue but have found a way to avoid it. Instead of disconnecting the camera plugs, pop off the metal plate that holds the back camera and pry it out of place, and unscrew the front camera and pop that out of place.
So far, all cameras on the last 4 I have worked on do work.