Could RQM test plan connect to test case in another project area?

No, link but duplicating @Rajat Singh is right.

How to copy http://pic.dhe.ibm.com/infocenter/clmhelp/v4r0m3/topic/com.ibm.rational.test.qm.doc/topics/c_copy_overview.html

Information related to depencies you can find here: https://jazz.net/wiki/bin/view/Main/RqmApi?errno=2#Compatibility

Picture 2 Test Plan Details:

I havent seen any such option in RQM to link test cases from different project area.
However, you can move the test cases from one project area to another by duplicating it and then can link them to the desired test plan.

Best Regards
Rajat

Hi

Below is the technote on how to create and manage your enhancement requests:
http://www-01.ibm.com/support/docview.wss?uid=swg21298482

Best Regards
Rajat