Are you using LDAP for user authentication or are you using local IDs on the NAS?
If local NAS authentication then your passwd and group files (etc\) need to have the same information as from the server mounting. So what ever they have on the server in the passwd and group files you need to have on the NAS passwd and group files. UID and GID have to match. Be careful that the syntax on the NAS group file is abit different from the server has listed. Once the passwd and group files are in sync then your nobody ownership issue will go away.
Also if you are not using NFSv4 then disable it. 🙂