To eleaborate:

For the Shimano Nexus 3 speed, only the indexing of 2nd gear matters, as long as the shifter gives more than enough travel for 1st and 3rd. 1st is when the cable is slack, and there is an overtravel spring in the operating plunger that keeps extra travel the other direction from being a problem. A front deraillier thumb shifter works nicely, and is much more robust than the shifter that comes with the hub. (which I broke on the test ride)

With the SA hub, indexing of all three gears is critical, so the shifter needs to have the correct travel/detent to match.