As a matter of fact, it has been done! Here and here
That said, there’s a certain level of sincerity involved with paid adoptables. However, an exchange of real world money is involved in the transaction. Which makes it more similar to a commission or, more definitely, a “packaged” commission.
To take Nix’s point a steps further, NFTs are tied to a blockchain. Basically put, an NFT is a receipt for a placement on a blockchain. Since these adoptables are not associated with any form of cryptocurrency or blockchain, the statement is misleading, perhaps even grossly so.