The material inserts are not teflon. They are co-molded of rubber and some form of PU or whatever hard material that can be co-molded with rubber. There are DIN specs on the hardness of plastic that make contact with the DIN spec interfaces on the binding. Rubber has a very high coefficient of friction.
As Bud sad for the toe insert, the same is true for the firmer heel insert. It is part of meeting DIN spec. It is there to isure that the boot sole can properly compress the brake, and will escape properly from the heel when there is a twist release at the toe.
The sole planer cannot be used on this material. However canting can be accomplished using canted lift plates, available from some shops that like Start Haus that stock the product. Screw adhesion and plating these new soles is a little tricky.
"Other" boots with rubber soles, like many of the AT boots that are now available with rubber inserts, also have to conform to shape and hardness to function with alpine bindings. Many of the new AT boots like BD Factors, or Dynafit Zeus, etc, either come with alpine compatible soles, they are shipped with touring soles that are not DIN binding compatible. Some manufacturers sell the product with the extra soles in the box, some sell them as add on purchases.
IMHO vibram soles are great for walking, and hiking. They do pose some interface problems with some bindings. I had a case last spring where a customer came in with a boot that had Lange vibram soles added on as lift plates, and we could not get a Marker Jester to properly release test. When the forward pressure was correctly adjusted the customer could not get the boot heel down into the heel cup of the binding to compress the heel tab to close. The heel cup was digging into the rubber on entry and exit. To check the effect of the vibram lift, I swapped the plate out with the same thickness standard material lift plate and the customer could get in and out of the binding and it passed the heel release test on our Huber machine. JFWIW, IMHO there will be a learning curve for ski retailers that are selling and servicing these products.