I found this KB for ONTAP 9 which say to use the top_client object.
I tried to check the instances using the harvest utility:
[root@sdt-poller util]# ./perf-counters-utility -host nltl-fas2520 -user admin -pass mySecret -f top_client -in
## Connected successfully to nltl-fas2520 running 92
This command does not support the 'top_client' object and other statistically tracked objects. Please use the "statistics start", "statistics stop", and "statistics show" commands.
If there is no instance list then Harvest is not going to be able to collect stats :-(.
I think a script that SSH to the cluster and do a 'statistics start', sleep 1hr, 'statistics stop', and 'statistics show' and send that to Graphite would be one way to go.
Probably not the answer you were looking for but hope this helps!
Solution Architect - 3rd Platform - Systems Engineering NetApp EMEA (and author of Harvest)