If I am not mistaken a sealed ratchet means that the cover plate is permanently attached to the ratchet so that there is a minimal chance of the ratcheting mechanism falling out of the head. Having small pieces of metal in certain areas of an aircraft engine, for example, would not be a good thing.
Actually, those are FOD ratchets.
They are sealed as well and the plate affixed with a rivet type fastener.
#F936FOD
#S936FOD
Std sealed rathet heads prevent dust and grime from getting in but not fluids per se'.
Thus why the "do not immerse" stamp.