If you don’t care about security and prefer to use only root account across all your machines, including on NFS shared file system, here is how you allow NFS clients root access on a NFS shared file system:
share -F nfs -o rw,root=host1:host2:host3 /nfs_share_dir
root=access_list option defines which host has root access to this specific NFS share.
Special thanks to Greg N. for pointed out
share_nfs man page.