You can use TDI for any integration where Domino is the primary source of primary target. It doesn't matter what Domino databases are involved. "Limited" means that you can't use TDI to integrate two non-Domino systems. Such as DB2 and Oracle, or SAP with Active Directory.
Here's the IBM description of the entitlement:
http://www-01.ibm.com/software/lotus/notesanddomino/tivoli-directory-integrator-entitlement.html