When you say "ribbed" do you mean that when you look at the brush side-on through the vent holes, it appears that there is an "arch" in the brush face (the axis of the arch is perpendicular to the comm) and the brush only touches the comm at the two ends of the "arch"?
If this is the case, then no, that's how it's supposed to be. It's the same in the "standard" silver-can 540's.
Wearing the brushes down so that they are in "full-face" contact shouldn't be necessary. It would be the equivalent of buying a set of serrated brushes for a rebuildable and running it in until all the serrations are gone.
Just use the same "water dip" method for the same length of time as you would a normal silver-can 540.