I use a dull draw knife for chasing a ring, but keep in mind that when you use this method it is no longer being used as a knife, as mentioned, it is a wedge. I am a true believer in "scary sharp" for all cutting tools, so don't try to use your dull knife for the same applications you would a sharp one.
just to repeat, if someone talks about using a dull drawknife for bow building, i am sure they are referreing to chasing rings and they are not using it for cutting, they are using it for wedging. When chasing a ring the dull knife will find the earlywood and pry off big sections without cutting into the next layer.
the only proper tool for cutting wood fibers is a very sharp blade.
I have two drawknives that i commonly use, one is dull and i have never sharpened it, this is used for chasing rings. the other is kept very sharp for all other stave reduction stuff.