How does it matter that it's traceable? Everyone knows the ships going in and out thanks to AIS. Many of these ships are already either falsely flagged, sanctioned, or just Iranian flagged. And as far as paying in rubles or yuan, this tells me that Iran doesn't think the shipping companies are willing to pay in either or think there's a safe/effective way to accept payment through those currencies.

I'm curious what makes your think these ships are unknown. There are 2 blockades in place and suspicion of mines in the conventional shipping route through Omani controlled waters.