Does the plugin support export of object metadata?
I want to export picklist values into another org, but the target org is missing some picklist values. Can the Plugin update the target org metadata with the missing picklist values and then export the data?
No. Migration/creation/changing of metadata is not supported, because this is the tool intended to deliver solution for data migration not for metadata.
You must have the same metadata in the source org and in the target org
unless you are using the Field Mapping.
For the field mapping you must have the mapped objects and fields in the target org, in this case the metadata of the source and the target can also be different.