Dear C.:
I am a medically retired (read disabled) Physician Assistant & Midwife Certified in both PA & AK. I have never heard of using the honey to help with a dry nose. I have used honey in the honeycomb all my life to ward off the flues and colds that winter brings, I don't know how it works but it does, about 1/2 teaspoon of honey with the honeycomb every morning and you chew on the honeycomb like it is gum until all the flavor is gone. It also seems to help with allergies.
This leads me to my next thought. It is quite possible that your son has allergies and that the dust that all furnaces grace our homes with in winter is getting to him and making it worse. As far as the picking at his nose goes, the mucous membrane is dried out and bothersome he could easily be picking in his sleep without even knowing it. It would make sense then that during the day you don't see the nose bleeds as he may not pick his nose on purpose.
The Nasal Saline mentioned by one Mom is a good idea. I have used it and it is nice because it keeps the membranes moist and flexible allowing them to heal and stop bleeding.
As far as the Vaseline goes anyone who is reading this should know NEVER put Vaseline in the nostrils. Vaseline is a petroleum product and breathing it in can cause pneumocystic pneumonia. No one wants that, it is a nasty type of pneumonia that is very difficult to get rid of. This applies not only to Vaseline but to Vicks vapor rub as well as it is petrolatum based.
Another think you might want to try along with the cool mist vaporizer is to take pans of water and put them on (if your heat vents are in the floor, or in front of [if they are in the wall) the heat vents, this will keep the house filled with much needed moisture throughout the day. I use a cheap set of mixing bowls that I picked up at a dollar store. It seems to work well and is not near as noisy (unless you have one of the silent vaporizers).
I don't know that I have helped you too much, but I hope you find something useful amidst my writings.
Take care and try to stay healthy while we all get hit with this heavy winter.
Best of everything,
J.