Never heard of fake rotors. Chains sure, same on eBay. If these rotors perform better than Zrace or Onirii I'm good since they cost the same.
With that said I have bought about 4 Shimano groupsets and there hasn't been an issue with counterfeit goods. Not sure if drive train stuff is being faked yet but doesn't seem like it.
On the other hand, counterfeit Shimano goods are a concern on Amazon including Ultegra/105 pedals and chains - all going for same price as original Shimano. If real Shimano chains and pedals are needed, I'll go to REI or other LBS.