I have a bag of sugar that was left on the cellar floor and is now damp and unusable for people. Maybe it would be like putting fruit into the bin? Eventually I hope to slowly get the whole bag of sugar into the bin.
I think sugar will be fine, IF you do not attract ants. Maybe extra energetic worms will work OT.
That was my first thought too: ants. You could mix a small amount with the worm food every time you have some kitchen scraps etc. I'm sure sugar will attract some extra microbes, just don't overdo that. I'm no chemist but will extra sugar cause fermentation??? We don't want that in our worm bin do we?
I know some will use sugar to help keep traditional compost hot over winter. It is devoid in nitrogen (C12 H22 O11) but I think it will act like a nitrogen / green source in the composting .
I have put sugar in my bin but it was in rather trivial amounts such as when it got spilled on the counter.