We get rich off of it by passing it off to Samura. They pay the Hogosha to do nasty things to Kishiro or assorted foreigners (Synth is just enough of a threat that they have the entire FA devoted to it), and while yes, the start and stop points aren't in Kusari territory they're very close (Tau-23 is only 50k and two and a half lanes from Kabukicho) and the transports who come through can be rather... rude (in character or out of it, it's pretty easy to distinguish). We'd be stealing from the transports as they marched through to teach them respect and make us piles of cash anyway, but if we can get the lesson in respect done outside of Kusari territory- and better yet, away from prying eyes- then all the better. Not like we're going very far to do it, after all (like I said before, 50k and 2.5 lanes from Kabukicho).
The ore gets to Rheinland one way or another. That part we couldn't care less about. They're outsiders, even if their outsiders the Emperor is somewhat fond of. The taking of ore by Samura, however, means that Samura gets the transport fee (quite a hefty fee at that) rather than some random disrespectful gaijin- and that is something that they pay us for.
Basically, it's Samura cutting in on the river of money that flows straight through Kusari, using the Hogosha to get their share for them. The transportation is done by Samura, as the Hogosha appear to be repninja'd hostile to Rheinland.
EDIT: I think I should mention that you are correct, blatant piracy is not the Hogosha way. Not in Kusari, anyway. But Tau-23 is not Kusari. We don't need to hide our operations there, as there is no one to hold us accountable for our actions. In Kusari proper we are a bit more careful about taking ore from transports- especially if the KNF or KSP are around.