After some detective work I have been able to get XnView to work with ghostscript again. I am not sure when it broke but I have a fix for it.
It appears that two of the environment variables inside of XnView were changed as follows.
GS_DLL -> XNVIEW_GS_DLL
GS_LIB -> XNVIEW_GS_LIB
As a result the [Environment] entries in XnViewPortable.ini located in the App\AppInfo\Launcher\ directory need to be changed to reflect this. The new entries should be:
If a developer could make this change in the distribution package, so that future upgrades do not break it again, it would be much appreciated.