User quota metrics (so user or group quota usage per qtree) are not collected by Harvest. When originally implementing I think I decided that such a level of detail would create too many metrics and lead to long load times in Graphite/Grafana if you tried to view them with a lot of users (i.e. thousands). But checking the API docs just now I couldn't find any OCUM API to get user quota info even if I wanted it!
So if you need this info you would be best to use the quota-report API to the cDOT cluster directly, parse it, and submit to Graphite. Because of the low demand it's not on my roadmap, but if you want to code it up you can share it here on communities and I can validate and include it as an 'extra' in a future release.
Cheers, Chris Madden
Storage Architect, NetApp EMEA (and author of Harvest)