Harvest does not have a feature to exclude collection of specific instances, but you can configure the Graphite server to drop them by using the blacklist feature. Details on how to set this up are in the Harvest 1.3 Administration guide on pg 24 " Use a blacklist to prevent visibility of temporary volumes [optional] ". If you have stale metrics you might also like to delete them as a one time action and setup in cron using details on pg 25 in "Purging inactive metrics from Graphite [optional]"
Hope this helps!
Cheers, Chris Madden
Solution Architect - 3rd Platform - Systems Engineering NetApp EMEA (and author of Harvest)