Hello nico68,
It is a bit late but I use RBE2 to model welding between two parts in Patran, usually node to node (I mean one to one). It is not important how you define independent and dependent node, but be sure to constraint 6 dof.
The thing is that this RBE2 MPC restraints traslations (forces) and rotations (torques) in the correct way.
Hope that helps you