From curiosity I downloaded the source code Viewnior and searched the code for “lcms” but didn’t find the usual statement about including lcms2.h, which means if it’s color-managed, it’s not using lcms, which would be highly unlikely for a linux application. I installed it anyway and opened a linear gamma png, which it displayed with the usual too-dark tonality for image viewers that aren’t color-managed. So Viewnior isn’t color-managed.
I’m guessing the automated microscope scans are output as more or less perceptually uniformly encoded images, so for the task you described, probably actual color management isn’t needed, though in this scenario what the monitor shows will vary from monitor to monitor.
Which jpgs do you mean? I uploaded two linear gamma pngs, one of which got turned into a highly posterized reduced-size sRGB jpeg - there are obvious discrete steps in the shadows, whereas in the original png there is a smooth continuous gradient from dark to light.