Of course no one is going to install a catch can in the actual charge hose line/path, and that oil Ironmonger is seeing has to be from the turbo oil seals.
But the OCCs do cut down on the oil mist getting into the combustion chambers from the recirculation of them into the intake manifold from the factory PCV system.
Why have BOTH whatever oil mist/vapor the factory system is dumping back into the intake manifold, in tandem with whatever is getting into the intake tract from the turbo oil seals dumping it into the charge pipes/hoses, all going into the chambers, and therefore onto the intake valves??