After resetting the video driver back to the default, I can now boot all the way. However, any attempt to reload Snap for OS/2 3.1.1 results in the inability to completely boot the system as before.
Well, I've got my 1280 by 1024 display resolution back, and at 65,536 colors, but scrolling with the wheel mouse is a bit stuttered.
I can live with it for now. Probably should file a bug report with SciTech.