What exactly is the purpose of the Oil Pump in an NP231? I get the obvious "it moves oil around" but to what and how? It just floats on the rear output shaft and doesn't seem to line up with any ports. So does it just "spray" oil at the rear chain? Seems rather pointless (though I'm sure it's not). I'm asking only out of curiosity/desire to understand.

I think it moves oil around by spraying oil at the chain..

It pumps oil up to the top of the tcase and forward to the planetary gears

Considering how tough these xfer cases are and how long the same basic design has been used, I'd say the design is pretty dang good.