Printer drivers are what tell your computer how to talk to the printer, since the NAS does not create the print job it does not need printer drivers - all it does is take the print job that is sent to it by the PC and pass it on to the printer.
Whatever features that are not working most likely require bi-directional communication between the PC and the printer which is not supported by the DNS-323 - all communications are unidirectional, ie. from the PC to the printer. As far as spooling goes, you can be sure that spooling does occur - print spooling is the process through which the print job is accepted from the PC, temporarily stored in the print queue on the disk, and then sent to the printer.
Try this - switch the printer off, send a print job, switch the PC off and then switch the printer on - if I'm right the print job will print even though the PC is off, thus proving that the print job was stored (or spooled) on the disks in the NAS.
Perhaps I should point out here that I am specifically referring to the print server functionality, because the situation as decribed could possibly change - there is a "shareport" application being developed for the DNS-323 which could possibly allow the USB port to be shared - since this would allow you to use it as a shared USB port rather than a print server, it would theoretically allow bi-directional communications, and might allow you to use the functionality not available through the print server.