Why not? You bought some equipment, so you received some private key from the manufacturer and as long as that manufacturer sells miners with unique private keys, it is possible to identify which customer mined which blocks. It is the same kind of proof like with Casascius coins: the private key is protected from viewing by anyone and if you want to sell that mining device to someone else, that person will be able to tell if that private key is still inside or was it revealed by scraping something, detaching some factory labels that has "warranty void if removed" or similar signs, etc.

Also, mining device don't have to lock coins on manufacturer's key, all that is needed is signing blocks with that key, for example in the same way as you can see in signet.