Hi Justin,
why do you think RC ignores certain settings for different aquisition techniques? There is no way RC can figure this out by itself - it’s not intelligent enough (yet) ! 
I would think that epty gps values are ignored, at least I never had any problems with this (that I am aware of).
I don’t know too much about priors, but I am pretty certain that they are used as starting-off point, so it might very well be a bit faster but also less prone to come up with an entirely wrong undistortion.