> To provide a greater degree of compatibility with NFSv3, which identified users and groups by 32-bit unsigned user identifiers and group identifiers, owner and group strings that consist of ASCII- encoded decimal numeric values with no leading zeros can be given a special interpretation by clients and servers that choose to provide such support. The receiver may treat such a user or group string as representing the same user as would be represented by an NFSv3 uid or gid having the corresponding numeric value.
I'm not sure how common this extension is, at least the Linux server and client support it out of the box. Isilon also supports it, but it must be explicitly enabled.