It’s possible to scuba dive without knowing how to swim, but I wouldn’t recommend it. You don’t need to use your arms whilst diving underwater like you do when swimming. But knowing how to swim makes it safe and is about being able to get yourself out of trouble, if anything goes wrong. Scuba diving is classed as a ‘dangerous sport,’ so why add risk to your enjoyment of your hobby for no reason? Be safe, don’t be sorry.