Neither Aperture libraries not iPhoto libraries can be stored on a NAS. The filesystem on the drive needs to be MacOS Extended (journaled) and the library needs to be on locally connected drive, because the internal databases do not support network transactions. You would be risking library corruption and data loss on a NAS. Also, the access time is much slower than on a locally connected drive, so the response time would be unnecessary slow, when working with large raw files.
See Apple's recommendation for Aperture - the same is true for iPhoto:
Use locally mounted Mac OS X Extended volumes for your Aperture library
To share a library among several users, move it to an external drive and set the "Ignore ownership on this volume" flag, see this document: iPhoto: Sharing libraries among multiple users
Local hard drives are becoming overly taxed with the amount of data from high res pictures.
How many photos are you talking about? Aperture has been designed to deal with really huge libraries, and 1or 2 TB library size is working for some posters here.
-- Léonie