Im not familiar with the fermenting process. That site says the fermentation process reduces sugar. 

From wikipedia

When used as feed for dairy cattle, alfalfa is often made into haylage by a process known as ensiling.[19] Rather then being dried to make dry hay, the alfalfa is chopped finely and fermented in silos, trenches, or bags, where the oxygen supply can be limited to promote fermentation.[52] The anaerobic fermentation of alfalfa allows it to retain high nutrient levels similar to those of fresh forage, and is also more palatable to dairy cattle than dry hay.[53] In many cases, alfalfa silage is inoculated with different strains of microorganisms to improve the fermentation quality and aerobic stability of the silage.[54][55]

The main issue I see with chaff is that it’s small pieces so the rabbits don’t require the chewing they would with strands of hay. It’s the chewing action that keeps their ever growing teeth worn down.

 High nutrient feed could actually be a problem for rabbits. They are designed to make their own essential nutrients by fermenting food in their own cecum. 

 Just a grass hay and occasional alfalfa hay would be enough for rabbits.
http://rabbit.org/the-importance-of-hay/