And what about all these arrancar? It seems as though with the current fighting that the Shinigami are now treating them as just evil enemies. I'm sure at the beginning of the series there was a more humane outlook on hollows. When you killed a hollow its soul would be released and would be able to go to SS. If that is the case then can't the arrancar who have been killed shed some light on what Aizen's plans are once they get to SS?
This is actually kinda complicated. Since Hitsugaya's explanation on the arrancar kinda imply that all the arrancar are made from Menos Grande type hollows having their masks ripped off.

And Menos hollows are formed from a bunch of hollows merging together. So by that extension, i'm assuming that for all the dead arrancar, when they are cleansed into soul society, they split back into the souls that made up the menos hollows in the first place, and so the personality of the arrancar is destroyed.