You can specify a file name or directory name in a quota entry and the quota is applied to the owner of that file or directory. The same is true for group quotas. So again, in a NFS only environment you don't need a user database. Here's a typical entry from our quota file:
/h1/s/sc/scl user 100M 100K
be careful with this syntax. when i had entries in this form i had problems where once the directory /h1/s/sc/scl would fill up, no writes were permitted for that user, anywhere on the filer. this included shared directories owned by him. but written to by others. yet not existing under his homedir.
scl user@/vol/vol1/h1/s/sc/scl 100M 100K
would have the effect of only applying to their homedir. that seems to be my experience.
-steve