Will low moisture harm a veneered MDF speaker?

You shouldn't have any problems, MDF is very stable and the veneer glues used today are fairly bulletproof. As long as the clearcoat finish is in good shape, so is the veneer. The worst thing you can do is get the speakers too close to the heat source or sunlight. Do not use cleaning/polishing products that say they will moisturize the finish (big pile of BS), contain petroleum distillates or silicone (Pledge), which leaves a greasy film and makes any repair/touch up very hard to do. If your speakers have an oiled finish then you will most likely want to re-oil them from time to time. Other than that, dust them often and enjoy your music.

I have a wood stove in my room as well. I run a humidifier in there 24/7. Keeping the air moist cuts down on static build up, a nasty winter gremlin...I have to fill the two tanks once a day, I have the humidistat set at about halfway, putting 2 gallons of water into the air. The stove is going a lot, compliments of a pretty chilly Northeast this Jan.