Yes, but you need to check what degree of ownership you have over your commissioned artwork. Websites like Upwork and DesignCrowd automatically give you full intellectual property rights while Fiverr only guarantees ownership rights unless you pay sellers for commercial rights. Before you commission an NFT, you need to decide whether you want to sell a single copy of that artwork or if you want to make multiple copies and sell the design elsewhere. You should also carefully check your legal rights with each freelancer website and with each seller to make sure you won’t run into any legal issues.