How to move or copy artifacts folder in DNG from one project area to another project area?

I'm not aware such feature exists. The best option would be using ReqIF files to export and import the requirements and folders. Note that the type system (including artifact types, attribute types, data types and link types) can be changed in the target project area due to the ReqIF import. Read the documents carefully so you won't get surprised by the "unexpected" result.
http://www-01.ibm.com/support/knowledgecenter/SSCP65_5.0.0/com.ibm.rational.rrm.help.doc/topics/r_reqif_format.html

We expect to support cross-project copy in the upcoming 601 release.  See https://jazz.net/jazz03/resource/itemName/com.ibm.team.workitem.WorkItem/44284.

Another thing to note about using ReqIF export/import is the need for RDF URI defined for each artifact type configuration. If you encounter duplicated artifact type / attribute / attribute type created after ReqIF import, you should look into the RDF URI configuration.

Here is an article addressing a possible outcome on ReqIF import:
https://jazz.net/downloads/rational-requirements-composer/releases/4.0.5?p=news#TOC_E
Perform a keyword search on ReqIF (Requirements Interchange Format)