As the oracle account is a local account I have created the user and group on TrueNAS with the same UID and GID values, but still cannot get the oracle account to access the mount
This is a local permission denied issue, i.e. on the client side.
NFS mounts are performed by root just like local file system mounts. The resulting access rights for ordinary users depend on the numeric user and group IDs on the client and the server side which ideally match.
NFS is machine to machine, not user to service like e.g. SMB. That’s why there is also no authentication up to and including version 3.