Just for fun.... Many years ago, a FLAPS (favorite local auto parts store) that used a bicycle for some of there deliveries, brought in a SA 3spd rear wheel from their delivery bike. The goy bringing it in was a little "sheepish" as he described what they had done to the hub. They assumed the oil filler nipple was some sort of bicycle grease zert, so they fashioned some sort of adapter and proceeded to pump the hub full of grease. BTW I don't know what kind of grease, but it was the nastiest, stickiest stuff you can imagine. Well, as you can guess, the hub no longer shifted into any gear.
I recall spending the better part of a morning at the parts bath trying to clean out the hub and its "guts". I don't remember if I had to replace anything or not, but I had them going again that afternoon. I do remember taking a flat spot and some blips out of the rim.
SO, I don't know about a coaster brake hub, but don't fill a SA 3spd hub with grease.
The bike was one of those rod brake, 28" wheel, double top tube Denalts. I always thought those were pretty cool. Weighed a TON, but I guess designed for use in Africa and India.
Brad Luecke
Columbia MO USA