The OAI-Harvester is purely documented. A bit general documentation can be found here: https://wiki.duraspace.org/display/DSDOC6x/OAI#OAI-OAI-PMH/OAI-OREHarvester(Client) But it contains the information the harvester would exists in XMLUI only. Nevertheless if I edit a collection in JSPUI I see a form regarding the oai harvester. Furthermore the documentation linked above contains configuration options that are missing in the configuration file (dspace/config/modules/oai.cfg) like oai.harvester.eperson.
The harvester command on the command line is not documented at all: https://wiki.duraspace.org/display/DSDOC6x/Command+Line+Operations
Some more documentation that seems to be XMLUI specific can be found here: https://wiki.duraspace.org/display/DSDOC6x/XMLUI+Configuration+and+Customization#XMLUIConfigurationandCustomization-HarvestingItemsfromXMLUIviaOAI-OREorOAI-PMH
Does the OAI-Harvester work for JSPUI and XMLUI? Are there any differences between the support in XMLUI and JSPUI? Can someone please describe its general approach? Are any cronjobs necessary to run the harvester regularly? What does the CLI option harvester is used for, what does it supports? ...