generally, yes, but you need to consider two more skills:
1. too close routings may introduce more line2line coupling, that means the capacitive loading of the signal may be bigger, so leave some space can be benificial.
2. pay attention to environmental noise coupling, sometimes for critical differential signals, ground shielding is necessary on both sides.
the dummy metal acts as the common node of the parasitic capacitance bet the diff pair.
theredore, the parasitic capacitance will be seen as series from the first input to the common node and from the common node to the other input.