CF tends to be strong along the grain axis, so you really DO NOT want anything "grinding" into it too much or upsetting the grain.

Use washers to prevent damage and if necessary do exactly as you've said and utilize another material that will not grind into the CF.

BTW:

In my old Funtana S90 I puchased and installed second party CF axles.

I did not need to do anything to the axle mount area... but one day because of a VERY hard landing, I did exactly as you said and sheared off the "tab" the axles bolt to.

I ended up gluing ( on both sides for appearances ) a small 1x1" square of CF over the broken area, after I put it back together... I then redrilled the axle holes through the new material, and finally added thin 1" CF rods alone each side of the square vertically.

I've since hit it even harder on bad landings and it has held up VERY well with no cracks or breaks.

So if you are concerned you can do something similiar, but I doubt you really need to... CF is stronger than you think.