Mike,
Using very general terms (I'm not familiar with US lubricators...) a hydrostatic lubricator can also be described as a "displacement" because these have a steam feed from the boiler which can be regulated. The steam is condensed back into water and, as every schoolboy knows, the oil floats on water so the oil is "displaced", via pipes to where the lubrication is desired. The feeds also have valves and sight glasses to enable the feed rate to be contolled.
Mechanical lubricators that I have encountered are driven from the motion, using rods, to a ratchet drive on the end of a cam encased in the lubricator which in turn activates plunger pumps to force the oil to where it is required. These feed points might also include a steam fed "atomiser" so the oil is delivered as a fine mist rather than a "blob".
This is a very general description only.
G