After hours of hammering away at the crash I mentioned at https://forums.unrealengine/showthread.php?53735-NVIDIA-GameWorks-Integration&p=543352&viewfull=1#post543352 for hours, I managed to find the problem specifically.
The crash only occurs in my scene when “VXGI Cone Tracing” is enabled in a translucent material. is in the current 4.12.2 build on the Nvidia Github that I redownloaded and recompiled from scratch tonight to make sure nothing else would interfere.