I don't know anything about your Golf, but the tube in question should not go to the intake manifold - it should go to the breather from the valve cover. As you know, there should be no significant vacuum at this point.
In order for the pressure regulator to function, the 'backside' of the regulating diaphram must be at atmospheric pressure. This is the purpose of the vent port. If the diaphram ruptures or leaks, though, you would have fuel pouring over the engine. So, it is routed instead into the vapor recirculating plumbing.
The pressure regulator itself is just designed to maintain a constant, high fuel pressure. There is no loop control there. The CIS injection modulates pressure and thus flow rate at the fuel distributor, mechanically coupled to the airflow meter underneath, and electrically fine-tuned via the EHA valve by the fuel injection control module, using loop inputs from the oxygen and other sensors.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7