The hub does need servicing, and is not greased for life! However, it can be lubricated with a thickish oil, just a few drops or so, run down into the axle, after removing the indicator rod (gear adjuster). This is the advice I obtained from Brompton technical services:
The Sturmey Archer hub only requires grease on the bearings and pinions (that are located on the planet cage/pinion assembly), the rest of the internals require a thick oil (such as wet conditions chain lubricant).
There are various sources available to show the correct manner for dismantling and re-assembling a 3-speed SA hub.