The modified Klamper on a Rohloff with Hope vented rotor worked well after many significant down slopes (>8%) with our heavily loaded tandem (camping on tour). We have 2 canti rim brakes in addition to the disc on the Rohloff. The Klamper caliper will not clear the Hope 3.3 mm rotor. I would call it a spacer, not a shim. The spacer should be at least 1.5 mm. Below is a drawing of the important parts of the caliper and a pic showing the result.
The metal buttons that hold the outer SS disc ring onto the Al carrier of the Hope disk came very close to the body of the caliper. This meant that the caliper had to be precisely centered else the buttons might scrape on the caliper body. The buttons rotate past the rear end of the caliper. In addition to machining the spacer from SS stock, I machined 20 mils off the rear end of the caliper body so that the arc of the buttons has significant clearance from the caliper body. That made positioning of the caliper much easier. It may be that a 2 mm spacer would result in sufficient clearance from the buttons so that you would not need to take of the 20 mils off of the body.
Don't know about the Santana rotor, the Hope rotor is the only vented rotor that can be attached to a Rohloff. All because of the much effort and testing of Thorn to find a disc brake suitable for a heavy tandem with a Rohloff. Thorn pairs this with a Hope hydraulic caliper, but hydraulics are a hassle with a break apart bike and for touring.
